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postgres/doc/src/sgml/func/func-info.sgml
Michael Paquier 97b101776c Add pg_get_multixact_stats() 
This new function exposes at SQL level some information related to
multixacts, not available until now.  This data is useful for monitoring
purposes, especially for workloads that make a heavy use of multixacts:
- num_mxids, number of MultiXact IDs in use.
- num_members, number of member entries in use.
- members_size, bytes used by num_members in pg_multixact/members/.
- oldest_multixact: oldest MultiXact still needed.

This patch has been originally proposed when MultiXactOffset was still
32 bits, to monitor wraparound.  This part is not relevant anymore since
bd8d9c9bdf that has widen MultiXactOffset to 64 bits.  The monitoring
of disk space usage for the members is still relevant.

Some tests are added to check this function, in the shape of one
isolation test with concurrent transactions that take a ROW SHARE lock,
and some SQL tests for pg_read_all_stats.  Some documentation is added
to explain some patterns that can come from the information provided by
the function.

Bump catalog version.

Author: Naga Appani <nagnrik@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Discussion: https://postgr.es/m/CA+QeY+AAsYK6WvBW4qYzHz4bahHycDAY_q5ECmHkEV_eB9ckzg@mail.gmail.com
2025-12-30 15:38:50 +09:00

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<sect1 id="functions-info">
<title>System Information Functions and Operators</title>
<para>
The functions described in this section are used to obtain various
information about a <productname>PostgreSQL</productname> installation.
</para>
<sect2 id="functions-info-session">
<title>Session Information Functions</title>
<para>
<xref linkend="functions-info-session-table"/> shows several
functions that extract session and system information.
</para>
<para>
In addition to the functions listed in this section, there are a number of
functions related to the statistics system that also provide system
information. See <xref linkend="monitoring-stats-functions"/> for more
information.
</para>
<table id="functions-info-session-table">
<title>Session Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_catalog</primary>
</indexterm>
<function>current_catalog</function>
<returnvalue>name</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>current_database</primary>
</indexterm>
<function>current_database</function> ()
<returnvalue>name</returnvalue>
</para>
<para>
Returns the name of the current database. (Databases are
called <quote>catalogs</quote> in the SQL standard,
so <function>current_catalog</function> is the standard's
spelling.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_query</primary>
</indexterm>
<function>current_query</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns the text of the currently executing query, as submitted
by the client (which might contain more than one statement).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_role</primary>
</indexterm>
<function>current_role</function>
<returnvalue>name</returnvalue>
</para>
<para>
This is equivalent to <function>current_user</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_schema</primary>
</indexterm>
<indexterm>
<primary>schema</primary>
<secondary>current</secondary>
</indexterm>
<function>current_schema</function>
<returnvalue>name</returnvalue>
</para>
<para role="func_signature">
<function>current_schema</function> ()
<returnvalue>name</returnvalue>
</para>
<para>
Returns the name of the schema that is first in the search path (or a
null value if the search path is empty). This is the schema that will
be used for any tables or other named objects that are created without
specifying a target schema.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_schemas</primary>
</indexterm>
<indexterm>
<primary>search path</primary>
<secondary>current</secondary>
</indexterm>
<function>current_schemas</function> ( <parameter>include_implicit</parameter> <type>boolean</type> )
<returnvalue>name[]</returnvalue>
</para>
<para>
Returns an array of the names of all schemas presently in the
effective search path, in their priority order. (Items in the current
<xref linkend="guc-search-path"/> setting that do not correspond to
existing, searchable schemas are omitted.) If the Boolean argument
is <literal>true</literal>, then implicitly-searched system schemas
such as <literal>pg_catalog</literal> are included in the result.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_user</primary>
</indexterm>
<indexterm>
<primary>user</primary>
<secondary>current</secondary>
</indexterm>
<function>current_user</function>
<returnvalue>name</returnvalue>
</para>
<para>
Returns the user name of the current execution context.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_client_addr</primary>
</indexterm>
<function>inet_client_addr</function> ()
<returnvalue>inet</returnvalue>
</para>
<para>
Returns the IP address of the current client,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_client_port</primary>
</indexterm>
<function>inet_client_port</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the IP port number of the current client,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_server_addr</primary>
</indexterm>
<function>inet_server_addr</function> ()
<returnvalue>inet</returnvalue>
</para>
<para>
Returns the IP address on which the server accepted the current
connection,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_server_port</primary>
</indexterm>
<function>inet_server_port</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the IP port number on which the server accepted the current
connection,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_backend_pid</primary>
</indexterm>
<function>pg_backend_pid</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the process ID of the server process attached to the current
session.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_blocking_pids</primary>
</indexterm>
<function>pg_blocking_pids</function> ( <type>integer</type> )
<returnvalue>integer[]</returnvalue>
</para>
<para>
Returns an array of the process ID(s) of the sessions that are
blocking the server process with the specified process ID from
acquiring a lock, or an empty array if there is no such server process
or it is not blocked.
</para>
<para>
One server process blocks another if it either holds a lock that
conflicts with the blocked process's lock request (hard block), or is
waiting for a lock that would conflict with the blocked process's lock
request and is ahead of it in the wait queue (soft block). When using
parallel queries the result always lists client-visible process IDs
(that is, <function>pg_backend_pid</function> results) even if the
actual lock is held or awaited by a child worker process. As a result
of that, there may be duplicated PIDs in the result. Also note that
when a prepared transaction holds a conflicting lock, it will be
represented by a zero process ID.
</para>
<para>
Frequent calls to this function could have some impact on database
performance, because it needs exclusive access to the lock manager's
shared state for a short time.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_conf_load_time</primary>
</indexterm>
<function>pg_conf_load_time</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the time when the server configuration files were last loaded.
If the current session was alive at the time, this will be the time
when the session itself re-read the configuration files (so the
reading will vary a little in different sessions). Otherwise it is
the time when the postmaster process re-read the configuration files.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_logfile</primary>
</indexterm>
<indexterm>
<primary>Logging</primary>
<secondary>pg_current_logfile function</secondary>
</indexterm>
<indexterm>
<primary>current_logfiles</primary>
<secondary>and the pg_current_logfile function</secondary>
</indexterm>
<indexterm>
<primary>Logging</primary>
<secondary>current_logfiles file and the pg_current_logfile
function</secondary>
</indexterm>
<function>pg_current_logfile</function> ( <optional> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the path name of the log file currently in use by the logging
collector. The path includes the <xref linkend="guc-log-directory"/>
directory and the individual log file name. The result
is <literal>NULL</literal> if the logging collector is disabled.
When multiple log files exist, each in a different
format, <function>pg_current_logfile</function> without an argument
returns the path of the file having the first format found in the
ordered list: <literal>stderr</literal>,
<literal>csvlog</literal>, <literal>jsonlog</literal>.
<literal>NULL</literal> is returned if no log file has any of these
formats.
To request information about a specific log file format, supply
either <literal>csvlog</literal>, <literal>jsonlog</literal> or
<literal>stderr</literal> as the
value of the optional parameter. The result is <literal>NULL</literal>
if the log format requested is not configured in
<xref linkend="guc-log-destination"/>.
The result reflects the contents of
the <filename>current_logfiles</filename> file.
</para>
<para>
This function is restricted to superusers and roles with privileges of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_loaded_modules</primary>
</indexterm>
<function>pg_get_loaded_modules</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>module_name</parameter> <type>text</type>,
<parameter>version</parameter> <type>text</type>,
<parameter>file_name</parameter> <type>text</type> )
</para>
<para>
Returns a list of the loadable modules that are loaded into the
current server session. The <parameter>module_name</parameter>
and <parameter>version</parameter> fields are NULL unless the
module author supplied values for them using
the <literal>PG_MODULE_MAGIC_EXT</literal> macro.
The <parameter>file_name</parameter> field gives the file
name of the module (shared library).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_my_temp_schema</primary>
</indexterm>
<function>pg_my_temp_schema</function> ()
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the OID of the current session's temporary schema, or zero if
it has none (because it has not created any temporary tables).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_other_temp_schema</primary>
</indexterm>
<function>pg_is_other_temp_schema</function> ( <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if the given OID is the OID of another session's
temporary schema. (This can be useful, for example, to exclude other
sessions' temporary tables from a catalog display.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_jit_available</primary>
</indexterm>
<function>pg_jit_available</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if a <acronym>JIT</acronym> compiler extension is
available (see <xref linkend="jit"/>) and the
<xref linkend="guc-jit"/> configuration parameter is set to
<literal>on</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_numa_available</primary>
</indexterm>
<function>pg_numa_available</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if the server has been compiled with <acronym>NUMA</acronym> support.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_listening_channels</primary>
</indexterm>
<function>pg_listening_channels</function> ()
<returnvalue>setof text</returnvalue>
</para>
<para>
Returns the set of names of asynchronous notification channels that
the current session is listening to.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_notification_queue_usage</primary>
</indexterm>
<function>pg_notification_queue_usage</function> ()
<returnvalue>double precision</returnvalue>
</para>
<para>
Returns the fraction (0&ndash;1) of the asynchronous notification
queue's maximum size that is currently occupied by notifications that
are waiting to be processed.
See <xref linkend="sql-listen"/> and <xref linkend="sql-notify"/>
for more information.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_postmaster_start_time</primary>
</indexterm>
<function>pg_postmaster_start_time</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the time when the server started.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_safe_snapshot_blocking_pids</primary>
</indexterm>
<function>pg_safe_snapshot_blocking_pids</function> ( <type>integer</type> )
<returnvalue>integer[]</returnvalue>
</para>
<para>
Returns an array of the process ID(s) of the sessions that are blocking
the server process with the specified process ID from acquiring a safe
snapshot, or an empty array if there is no such server process or it
is not blocked.
</para>
<para>
A session running a <literal>SERIALIZABLE</literal> transaction blocks
a <literal>SERIALIZABLE READ ONLY DEFERRABLE</literal> transaction
from acquiring a snapshot until the latter determines that it is safe
to avoid taking any predicate locks. See
<xref linkend="xact-serializable"/> for more information about
serializable and deferrable transactions.
</para>
<para>
Frequent calls to this function could have some impact on database
performance, because it needs access to the predicate lock manager's
shared state for a short time.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_trigger_depth</primary>
</indexterm>
<function>pg_trigger_depth</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the current nesting level
of <productname>PostgreSQL</productname> triggers (0 if not called,
directly or indirectly, from inside a trigger).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>session_user</primary>
</indexterm>
<function>session_user</function>
<returnvalue>name</returnvalue>
</para>
<para>
Returns the session user's name.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>system_user</primary>
</indexterm>
<function>system_user</function>
<returnvalue>text</returnvalue>
</para>
<para>
Returns the authentication method and the identity (if any) that the
user presented during the authentication cycle before they were
assigned a database role. It is represented as
<literal>auth_method:identity</literal> or
<literal>NULL</literal> if the user has not been authenticated (for
example if <link linkend="auth-trust">Trust authentication</link> has
been used).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>user</primary>
</indexterm>
<function>user</function>
<returnvalue>name</returnvalue>
</para>
<para>
This is equivalent to <function>current_user</function>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<function>current_catalog</function>,
<function>current_role</function>,
<function>current_schema</function>,
<function>current_user</function>,
<function>session_user</function>,
and <function>user</function> have special syntactic status
in <acronym>SQL</acronym>: they must be called without trailing
parentheses. In PostgreSQL, parentheses can optionally be used with
<function>current_schema</function>, but not with the others.
</para>
</note>
<para>
The <function>session_user</function> is normally the user who initiated
the current database connection; but superusers can change this setting
with <xref linkend="sql-set-session-authorization"/>.
The <function>current_user</function> is the user identifier
that is applicable for permission checking. Normally it is equal
to the session user, but it can be changed with
<xref linkend="sql-set-role"/>.
It also changes during the execution of
functions with the attribute <literal>SECURITY DEFINER</literal>.
In Unix parlance, the session user is the <quote>real user</quote> and
the current user is the <quote>effective user</quote>.
<function>current_role</function> and <function>user</function> are
synonyms for <function>current_user</function>. (The SQL standard draws
a distinction between <function>current_role</function>
and <function>current_user</function>, but <productname>PostgreSQL</productname>
does not, since it unifies users and roles into a single kind of entity.)
</para>
</sect2>
<sect2 id="functions-info-access">
<title>Access Privilege Inquiry Functions</title>
<indexterm>
<primary>privilege</primary>
<secondary>querying</secondary>
</indexterm>
<para>
<xref linkend="functions-info-access-table"/> lists functions that
allow querying object access privileges programmatically.
(See <xref linkend="ddl-priv"/> for more information about
privileges.)
In these functions, the user whose privileges are being inquired about
can be specified by name or by OID
(<structname>pg_authid</structname>.<structfield>oid</structfield>), or if
the name is given as <literal>public</literal> then the privileges of the
PUBLIC pseudo-role are checked. Also, the <parameter>user</parameter>
argument can be omitted entirely, in which case
the <function>current_user</function> is assumed.
The object that is being inquired about can be specified either by name or
by OID, too. When specifying by name, a schema name can be included if
relevant.
The access privilege of interest is specified by a text string, which must
evaluate to one of the appropriate privilege keywords for the object's type
(e.g., <literal>SELECT</literal>). Optionally, <literal>WITH GRANT
OPTION</literal> can be added to a privilege type to test whether the
privilege is held with grant option. Also, multiple privilege types can be
listed separated by commas, in which case the result will be true if any of
the listed privileges is held. (Case of the privilege string is not
significant, and extra whitespace is allowed between but not within
privilege names.)
Some examples:
<programlisting>
SELECT has_table_privilege('myschema.mytable', 'select');
SELECT has_table_privilege('joe', 'mytable', 'INSERT, SELECT WITH GRANT OPTION');
</programlisting>
</para>
<table id="functions-info-access-table">
<title>Access Privilege Inquiry Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_any_column_privilege</primary>
</indexterm>
<function>has_any_column_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for any column of table?
This succeeds either if the privilege is held for the whole table, or
if there is a column-level grant of the privilege for at least one
column.
Allowable privilege types are
<literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_column_privilege</primary>
</indexterm>
<function>has_column_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>column</parameter> <type>text</type> or <type>smallint</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for the specified table column?
This succeeds either if the privilege is held for the whole table, or
if there is a column-level grant of the privilege for the column.
The column can be specified by name or by attribute number
(<structname>pg_attribute</structname>.<structfield>attnum</structfield>).
Allowable privilege types are
<literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_database_privilege</primary>
</indexterm>
<function>has_database_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>database</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for database?
Allowable privilege types are
<literal>CREATE</literal>,
<literal>CONNECT</literal>,
<literal>TEMPORARY</literal>, and
<literal>TEMP</literal> (which is equivalent to
<literal>TEMPORARY</literal>).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_foreign_data_wrapper_privilege</primary>
</indexterm>
<function>has_foreign_data_wrapper_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>fdw</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for foreign-data wrapper?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_function_privilege</primary>
</indexterm>
<function>has_function_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>function</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for function?
The only allowable privilege type is <literal>EXECUTE</literal>.
</para>
<para>
When specifying a function by name rather than by OID, the allowed
input is the same as for the <type>regprocedure</type> data type (see
<xref linkend="datatype-oid"/>).
An example is:
<programlisting>
SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_language_privilege</primary>
</indexterm>
<function>has_language_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>language</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for language?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_largeobject_privilege</primary>
</indexterm>
<function>has_largeobject_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>largeobject</parameter> <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for large object?
Allowable privilege types are
<literal>SELECT</literal> and <literal>UPDATE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_parameter_privilege</primary>
</indexterm>
<function>has_parameter_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>parameter</parameter> <type>text</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for configuration parameter?
The parameter name is case-insensitive.
Allowable privilege types are <literal>SET</literal>
and <literal>ALTER SYSTEM</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_schema_privilege</primary>
</indexterm>
<function>has_schema_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>schema</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for schema?
Allowable privilege types are
<literal>CREATE</literal> and
<literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_sequence_privilege</primary>
</indexterm>
<function>has_sequence_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>sequence</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for sequence?
Allowable privilege types are
<literal>USAGE</literal>,
<literal>SELECT</literal>, and
<literal>UPDATE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_server_privilege</primary>
</indexterm>
<function>has_server_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>server</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for foreign server?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_table_privilege</primary>
</indexterm>
<function>has_table_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for table?
Allowable privilege types
are <literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, <literal>DELETE</literal>,
<literal>TRUNCATE</literal>, <literal>REFERENCES</literal>,
<literal>TRIGGER</literal>, and <literal>MAINTAIN</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_tablespace_privilege</primary>
</indexterm>
<function>has_tablespace_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>tablespace</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for tablespace?
The only allowable privilege type is <literal>CREATE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_type_privilege</primary>
</indexterm>
<function>has_type_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>type</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for data type?
The only allowable privilege type is <literal>USAGE</literal>.
When specifying a type by name rather than by OID, the allowed input
is the same as for the <type>regtype</type> data type (see
<xref linkend="datatype-oid"/>).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_has_role</primary>
</indexterm>
<function>pg_has_role</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>role</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for role?
Allowable privilege types are
<literal>MEMBER</literal>, <literal>USAGE</literal>,
and <literal>SET</literal>.
<literal>MEMBER</literal> denotes direct or indirect membership in
the role without regard to what specific privileges may be conferred.
<literal>USAGE</literal> denotes whether the privileges of the role
are immediately available without doing <command>SET ROLE</command>,
while <literal>SET</literal> denotes whether it is possible to change
to the role using the <literal>SET ROLE</literal> command.
<literal>WITH ADMIN OPTION</literal> or <literal>WITH GRANT
OPTION</literal> can be added to any of these privilege types to
test whether the <literal>ADMIN</literal> privilege is held (all
six spellings test the same thing).
This function does not allow the special case of
setting <parameter>user</parameter> to <literal>public</literal>,
because the PUBLIC pseudo-role can never be a member of real roles.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>row_security_active</primary>
</indexterm>
<function>row_security_active</function> (
<parameter>table</parameter> <type>text</type> or <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is row-level security active for the specified table in the context of
the current user and current environment?
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-aclitem-op-table"/> shows the operators
available for the <type>aclitem</type> type, which is the catalog
representation of access privileges. See <xref linkend="ddl-priv"/>
for information about how to read access privilege values.
</para>
<table id="functions-aclitem-op-table">
<title><type>aclitem</type> Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclitemeq</primary>
</indexterm>
<type>aclitem</type> <literal>=</literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are <type>aclitem</type>s equal? (Notice that
type <type>aclitem</type> lacks the usual set of comparison
operators; it has only equality. In turn, <type>aclitem</type>
arrays can only be compared for equality.)
</para>
<para>
<literal>'calvin=r*w/hobbes'::aclitem = 'calvin=r*w*/hobbes'::aclitem</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclcontains</primary>
</indexterm>
<type>aclitem[]</type> <literal>@&gt;</literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does array contain the specified privileges? (This is true if there
is an array entry that matches the <type>aclitem</type>'s grantee and
grantor, and has at least the specified set of privileges.)
</para>
<para>
<literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] @&gt; 'calvin=r*/hobbes'::aclitem</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>aclitem[]</type> <literal>~</literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
This is a deprecated alias for <literal>@&gt;</literal>.
</para>
<para>
<literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] ~ 'calvin=r*/hobbes'::aclitem</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-aclitem-fn-table"/> shows some additional
functions to manage the <type>aclitem</type> type.
</para>
<table id="functions-aclitem-fn-table">
<title><type>aclitem</type> Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>acldefault</primary>
</indexterm>
<function>acldefault</function> (
<parameter>type</parameter> <type>"char"</type>,
<parameter>ownerId</parameter> <type>oid</type> )
<returnvalue>aclitem[]</returnvalue>
</para>
<para>
Constructs an <type>aclitem</type> array holding the default access
privileges for an object of type <parameter>type</parameter> belonging
to the role with OID <parameter>ownerId</parameter>. This represents
the access privileges that will be assumed when an object's
<acronym>ACL</acronym> entry is null. (The default access privileges
are described in <xref linkend="ddl-priv"/>.)
The <parameter>type</parameter> parameter must be one of
'c' for <literal>COLUMN</literal>,
'r' for <literal>TABLE</literal> and table-like objects,
's' for <literal>SEQUENCE</literal>,
'd' for <literal>DATABASE</literal>,
'f' for <literal>FUNCTION</literal> or <literal>PROCEDURE</literal>,
'l' for <literal>LANGUAGE</literal>,
'L' for <literal>LARGE OBJECT</literal>,
'n' for <literal>SCHEMA</literal>,
'p' for <literal>PARAMETER</literal>,
't' for <literal>TABLESPACE</literal>,
'F' for <literal>FOREIGN DATA WRAPPER</literal>,
'S' for <literal>FOREIGN SERVER</literal>,
or
'T' for <literal>TYPE</literal> or <literal>DOMAIN</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclexplode</primary>
</indexterm>
<function>aclexplode</function> ( <type>aclitem[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>grantor</parameter> <type>oid</type>,
<parameter>grantee</parameter> <type>oid</type>,
<parameter>privilege_type</parameter> <type>text</type>,
<parameter>is_grantable</parameter> <type>boolean</type> )
</para>
<para>
Returns the <type>aclitem</type> array as a set of rows.
If the grantee is the pseudo-role PUBLIC, it is represented by zero in
the <parameter>grantee</parameter> column. Each granted privilege is
represented as <literal>SELECT</literal>, <literal>INSERT</literal>,
etc (see <xref linkend="privilege-abbrevs-table"/> for a full list).
Note that each privilege is broken out as a separate row, so
only one keyword appears in the <parameter>privilege_type</parameter>
column.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>makeaclitem</primary>
</indexterm>
<function>makeaclitem</function> (
<parameter>grantee</parameter> <type>oid</type>,
<parameter>grantor</parameter> <type>oid</type>,
<parameter>privileges</parameter> <type>text</type>,
<parameter>is_grantable</parameter> <type>boolean</type> )
<returnvalue>aclitem</returnvalue>
</para>
<para>
Constructs an <type>aclitem</type> with the given properties.
<parameter>privileges</parameter> is a comma-separated list of
privilege names such as <literal>SELECT</literal>,
<literal>INSERT</literal>, etc, all of which are set in the
result. (Case of the privilege string is not significant, and
extra whitespace is allowed between but not within privilege
names.)
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-schema">
<title>Schema Visibility Inquiry Functions</title>
<para>
<xref linkend="functions-info-schema-table"/> shows functions that
determine whether a certain object is <firstterm>visible</firstterm> in the
current schema search path.
For example, a table is said to be visible if its
containing schema is in the search path and no table of the same
name appears earlier in the search path. This is equivalent to the
statement that the table can be referenced by name without explicit
schema qualification. Thus, to list the names of all visible tables:
<programlisting>
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
</programlisting>
For functions and operators, an object in the search path is said to be
visible if there is no object of the same name <emphasis>and argument data
type(s)</emphasis> earlier in the path. For operator classes and families,
both the name and the associated index access method are considered.
</para>
<indexterm>
<primary>search path</primary>
<secondary>object visibility</secondary>
</indexterm>
<table id="functions-info-schema-table">
<title>Schema Visibility Inquiry Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_collation_is_visible</primary>
</indexterm>
<function>pg_collation_is_visible</function> ( <parameter>collation</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is collation visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_conversion_is_visible</primary>
</indexterm>
<function>pg_conversion_is_visible</function> ( <parameter>conversion</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is conversion visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_function_is_visible</primary>
</indexterm>
<function>pg_function_is_visible</function> ( <parameter>function</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is function visible in search path?
(This also works for procedures and aggregates.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_opclass_is_visible</primary>
</indexterm>
<function>pg_opclass_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator class visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_operator_is_visible</primary>
</indexterm>
<function>pg_operator_is_visible</function> ( <parameter>operator</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_opfamily_is_visible</primary>
</indexterm>
<function>pg_opfamily_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator family visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_statistics_obj_is_visible</primary>
</indexterm>
<function>pg_statistics_obj_is_visible</function> ( <parameter>stat</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is statistics object visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_table_is_visible</primary>
</indexterm>
<function>pg_table_is_visible</function> ( <parameter>table</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is table visible in search path?
(This works for all types of relations, including views, materialized
views, indexes, sequences and foreign tables.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_config_is_visible</primary>
</indexterm>
<function>pg_ts_config_is_visible</function> ( <parameter>config</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search configuration visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_dict_is_visible</primary>
</indexterm>
<function>pg_ts_dict_is_visible</function> ( <parameter>dict</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search dictionary visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_parser_is_visible</primary>
</indexterm>
<function>pg_ts_parser_is_visible</function> ( <parameter>parser</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search parser visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_template_is_visible</primary>
</indexterm>
<function>pg_ts_template_is_visible</function> ( <parameter>template</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search template visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_type_is_visible</primary>
</indexterm>
<function>pg_type_is_visible</function> ( <parameter>type</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is type (or domain) visible in search path?
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
All these functions require object OIDs to identify the object to be
checked. If you want to test an object by name, it is convenient to use
the OID alias types (<type>regclass</type>, <type>regtype</type>,
<type>regprocedure</type>, <type>regoperator</type>, <type>regconfig</type>,
or <type>regdictionary</type>),
for example:
<programlisting>
SELECT pg_type_is_visible('myschema.widget'::regtype);
</programlisting>
Note that it would not make much sense to test a non-schema-qualified
type name in this way &mdash; if the name can be recognized at all, it must be visible.
</para>
</sect2>
<sect2 id="functions-info-catalog">
<title>System Catalog Information Functions</title>
<para>
<xref linkend="functions-info-catalog-table"/> lists functions that
extract information from the system catalogs.
</para>
<table id="functions-info-catalog-table">
<title>System Catalog Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry id="format-type" xreflabel="format_type" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>format_type</primary>
</indexterm>
<function>format_type</function> ( <parameter>type</parameter> <type>oid</type>, <parameter>typemod</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the SQL name for a data type that is identified by its type
OID and possibly a type modifier. Pass NULL for the type modifier if
no specific modifier is known.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_basetype</primary>
</indexterm>
<function>pg_basetype</function> ( <type>regtype</type> )
<returnvalue>regtype</returnvalue>
</para>
<para>
Returns the OID of the base type of a domain identified by its
type OID. If the argument is the OID of a non-domain type,
returns the argument as-is. Returns NULL if the argument is
not a valid type OID. If there's a chain of domain dependencies,
it will recurse until finding the base type.
</para>
<para>
Assuming <literal>CREATE DOMAIN mytext AS text</literal>:
</para>
<para>
<literal>pg_basetype('mytext'::regtype)</literal>
<returnvalue>text</returnvalue>
</para></entry>
</row>
<row>
<entry id="pg-char-to-encoding" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_char_to_encoding</primary>
</indexterm>
<function>pg_char_to_encoding</function> ( <parameter>encoding</parameter> <type>name</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Converts the supplied encoding name into an integer representing the
internal identifier used in some system catalog tables.
Returns <literal>-1</literal> if an unknown encoding name is provided.
</para></entry>
</row>
<row>
<entry id="pg-encoding-to-char" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_encoding_to_char</primary>
</indexterm>
<function>pg_encoding_to_char</function> ( <parameter>encoding</parameter> <type>integer</type> )
<returnvalue>name</returnvalue>
</para>
<para>
Converts the integer used as the internal identifier of an encoding in some
system catalog tables into a human-readable string.
Returns an empty string if an invalid encoding number is provided.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_catalog_foreign_keys</primary>
</indexterm>
<function>pg_get_catalog_foreign_keys</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>fktable</parameter> <type>regclass</type>,
<parameter>fkcols</parameter> <type>text[]</type>,
<parameter>pktable</parameter> <type>regclass</type>,
<parameter>pkcols</parameter> <type>text[]</type>,
<parameter>is_array</parameter> <type>boolean</type>,
<parameter>is_opt</parameter> <type>boolean</type> )
</para>
<para>
Returns a set of records describing the foreign key relationships
that exist within the <productname>PostgreSQL</productname> system
catalogs.
The <parameter>fktable</parameter> column contains the name of the
referencing catalog, and the <parameter>fkcols</parameter> column
contains the name(s) of the referencing column(s). Similarly,
the <parameter>pktable</parameter> column contains the name of the
referenced catalog, and the <parameter>pkcols</parameter> column
contains the name(s) of the referenced column(s).
If <parameter>is_array</parameter> is true, the last referencing
column is an array, each of whose elements should match some entry
in the referenced catalog.
If <parameter>is_opt</parameter> is true, the referencing column(s)
are allowed to contain zeroes instead of a valid reference.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_constraintdef</primary>
</indexterm>
<function>pg_get_constraintdef</function> ( <parameter>constraint</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a constraint.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_expr</primary>
</indexterm>
<function>pg_get_expr</function> ( <parameter>expr</parameter> <type>pg_node_tree</type>, <parameter>relation</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Decompiles the internal form of an expression stored in the system
catalogs, such as the default value for a column. If the expression
might contain Vars, specify the OID of the relation they refer to as
the second parameter; if no Vars are expected, passing zero is
sufficient.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_functiondef</primary>
</indexterm>
<function>pg_get_functiondef</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a function or procedure.
(This is a decompiled reconstruction, not the original text
of the command.)
The result is a complete <command>CREATE OR REPLACE FUNCTION</command>
or <command>CREATE OR REPLACE PROCEDURE</command> statement.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_arguments</primary>
</indexterm>
<function>pg_get_function_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the argument list of a function or procedure, in the form
it would need to appear in within <command>CREATE FUNCTION</command>
(including default values).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_identity_arguments</primary>
</indexterm>
<function>pg_get_function_identity_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the argument list necessary to identify a function or
procedure, in the form it would need to appear in within commands such
as <command>ALTER FUNCTION</command>. This form omits default values.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_result</primary>
</indexterm>
<function>pg_get_function_result</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the <literal>RETURNS</literal> clause of a function, in
the form it would need to appear in within <command>CREATE
FUNCTION</command>. Returns <literal>NULL</literal> for a procedure.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_indexdef</primary>
</indexterm>
<function>pg_get_indexdef</function> ( <parameter>index</parameter> <type>oid</type> <optional>, <parameter>column</parameter> <type>integer</type>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for an index.
(This is a decompiled reconstruction, not the original text
of the command.) If <parameter>column</parameter> is supplied and is
not zero, only the definition of that column is reconstructed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_keywords</primary>
</indexterm>
<function>pg_get_keywords</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>word</parameter> <type>text</type>,
<parameter>catcode</parameter> <type>"char"</type>,
<parameter>barelabel</parameter> <type>boolean</type>,
<parameter>catdesc</parameter> <type>text</type>,
<parameter>baredesc</parameter> <type>text</type> )
</para>
<para>
Returns a set of records describing the SQL keywords recognized by the
server. The <parameter>word</parameter> column contains the
keyword. The <parameter>catcode</parameter> column contains a
category code: <literal>U</literal> for an unreserved
keyword, <literal>C</literal> for a keyword that can be a column
name, <literal>T</literal> for a keyword that can be a type or
function name, or <literal>R</literal> for a fully reserved keyword.
The <parameter>barelabel</parameter> column
contains <literal>true</literal> if the keyword can be used as
a <quote>bare</quote> column label in <command>SELECT</command> lists,
or <literal>false</literal> if it can only be used
after <literal>AS</literal>.
The <parameter>catdesc</parameter> column contains a
possibly-localized string describing the keyword's category.
The <parameter>baredesc</parameter> column contains a
possibly-localized string describing the keyword's column label status.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_partkeydef</primary>
</indexterm>
<function>pg_get_partkeydef</function> ( <parameter>table</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the definition of a partitioned table's partition
key, in the form it would have in the <literal>PARTITION
BY</literal> clause of <command>CREATE TABLE</command>.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_ruledef</primary>
</indexterm>
<function>pg_get_ruledef</function> ( <parameter>rule</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a rule.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_serial_sequence</primary>
</indexterm>
<function>pg_get_serial_sequence</function> ( <parameter>table</parameter> <type>text</type>, <parameter>column</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the name of the sequence associated with a column,
or NULL if no sequence is associated with the column.
If the column is an identity column, the associated sequence is the
sequence internally created for that column.
For columns created using one of the serial types
(<type>serial</type>, <type>smallserial</type>, <type>bigserial</type>),
it is the sequence created for that serial column definition.
In the latter case, the association can be modified or removed
with <command>ALTER SEQUENCE OWNED BY</command>.
(This function probably should have been
called <function>pg_get_owned_sequence</function>; its current name
reflects the fact that it has historically been used with serial-type
columns.) The first parameter is a table name with optional
schema, and the second parameter is a column name. Because the first
parameter potentially contains both schema and table names, it is
parsed per usual SQL rules, meaning it is lower-cased by default.
The second parameter, being just a column name, is treated literally
and so has its case preserved. The result is suitably formatted
for passing to the sequence functions (see
<xref linkend="functions-sequence"/>).
</para>
<para>
A typical use is in reading the current value of the sequence for an
identity or serial column, for example:
<programlisting>
SELECT currval(pg_get_serial_sequence('sometable', 'id'));
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_statisticsobjdef</primary>
</indexterm>
<function>pg_get_statisticsobjdef</function> ( <parameter>statobj</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for an extended statistics object.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_triggerdef</primary>
</indexterm>
<function>pg_get_triggerdef</function> ( <parameter>trigger</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a trigger.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_userbyid</primary>
</indexterm>
<function>pg_get_userbyid</function> ( <parameter>role</parameter> <type>oid</type> )
<returnvalue>name</returnvalue>
</para>
<para>
Returns a role's name given its OID.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_viewdef</primary>
</indexterm>
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view. (This is a decompiled reconstruction, not
the original text of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type>, <parameter>wrap_column</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view. (This is a decompiled reconstruction, not
the original text of the command.) In this form of the function,
pretty-printing is always enabled, and long lines are wrapped to try
to keep them shorter than the specified number of columns.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>text</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view, working from a textual name for the view
rather than its OID. (This is deprecated; use the OID variant
instead.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_index_column_has_property</primary>
</indexterm>
<function>pg_index_column_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>column</parameter> <type>integer</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index column has the named property.
Common index column properties are listed in
<xref linkend="functions-info-index-column-props"/>.
(Note that extension access methods can define additional property
names for their indexes.)
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID or column
number does not identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_index_has_property</primary>
</indexterm>
<function>pg_index_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index has the named property.
Common index properties are listed in
<xref linkend="functions-info-index-props"/>.
(Note that extension access methods can define additional property
names for their indexes.)
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID does not
identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_indexam_has_property</primary>
</indexterm>
<function>pg_indexam_has_property</function> ( <parameter>am</parameter> <type>oid</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index access method has the named property.
Access method properties are listed in
<xref linkend="functions-info-indexam-props"/>.
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID does not
identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_options_to_table</primary>
</indexterm>
<function>pg_options_to_table</function> ( <parameter>options_array</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>option_name</parameter> <type>text</type>,
<parameter>option_value</parameter> <type>text</type> )
</para>
<para>
Returns the set of storage options represented by a value from
<structname>pg_class</structname>.<structfield>reloptions</structfield> or
<structname>pg_attribute</structname>.<structfield>attoptions</structfield>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_settings_get_flags</primary>
</indexterm>
<function>pg_settings_get_flags</function> ( <parameter>guc</parameter> <type>text</type> )
<returnvalue>text[]</returnvalue>
</para>
<para>
Returns an array of the flags associated with the given GUC, or
<literal>NULL</literal> if it does not exist. The result is
an empty array if the GUC exists but there are no flags to show.
Only the most useful flags listed in
<xref linkend="functions-pg-settings-flags"/> are exposed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_databases</primary>
</indexterm>
<function>pg_tablespace_databases</function> ( <parameter>tablespace</parameter> <type>oid</type> )
<returnvalue>setof oid</returnvalue>
</para>
<para>
Returns the set of OIDs of databases that have objects stored in the
specified tablespace. If this function returns any rows, the
tablespace is not empty and cannot be dropped. To identify the specific
objects populating the tablespace, you will need to connect to the
database(s) identified by <function>pg_tablespace_databases</function>
and query their <structname>pg_class</structname> catalogs.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_location</primary>
</indexterm>
<function>pg_tablespace_location</function> ( <parameter>tablespace</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the file system path that this tablespace is located in.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_typeof</primary>
</indexterm>
<function>pg_typeof</function> ( <type>"any"</type> )
<returnvalue>regtype</returnvalue>
</para>
<para>
Returns the OID of the data type of the value that is passed to it.
This can be helpful for troubleshooting or dynamically constructing
SQL queries. The function is declared as
returning <type>regtype</type>, which is an OID alias type (see
<xref linkend="datatype-oid"/>); this means that it is the same as an
OID for comparison purposes but displays as a type name.
</para>
<para>
<literal>pg_typeof(33)</literal>
<returnvalue>integer</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>COLLATION FOR</primary>
</indexterm>
<function>COLLATION FOR</function> ( <type>"any"</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the name of the collation of the value that is passed to it.
The value is quoted and schema-qualified if necessary. If no
collation was derived for the argument expression,
then <literal>NULL</literal> is returned. If the argument is not of a
collatable data type, then an error is raised.
</para>
<para>
<literal>COLLATION FOR ('foo'::text)</literal>
<returnvalue>"default"</returnvalue>
</para>
<para>
<literal>COLLATION FOR ('foo' COLLATE "de_DE")</literal>
<returnvalue>"de_DE"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regclass</primary>
</indexterm>
<function>to_regclass</function> ( <type>text</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Translates a textual relation name to its OID. A similar result is
obtained by casting the string to type <type>regclass</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regdatabase</primary>
</indexterm>
<function>to_regdatabase</function> ( <type>text</type> )
<returnvalue>regdatabase</returnvalue>
</para>
<para>
Translates a textual database name to its OID. A similar result is
obtained by casting the string to type <type>regdatabase</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regcollation</primary>
</indexterm>
<function>to_regcollation</function> ( <type>text</type> )
<returnvalue>regcollation</returnvalue>
</para>
<para>
Translates a textual collation name to its OID. A similar result is
obtained by casting the string to type <type>regcollation</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regnamespace</primary>
</indexterm>
<function>to_regnamespace</function> ( <type>text</type> )
<returnvalue>regnamespace</returnvalue>
</para>
<para>
Translates a textual schema name to its OID. A similar result is
obtained by casting the string to type <type>regnamespace</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regoper</primary>
</indexterm>
<function>to_regoper</function> ( <type>text</type> )
<returnvalue>regoper</returnvalue>
</para>
<para>
Translates a textual operator name to its OID. A similar result is
obtained by casting the string to type <type>regoper</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found or is ambiguous.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regoperator</primary>
</indexterm>
<function>to_regoperator</function> ( <type>text</type> )
<returnvalue>regoperator</returnvalue>
</para>
<para>
Translates a textual operator name (with parameter types) to its OID. A similar result is
obtained by casting the string to type <type>regoperator</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regproc</primary>
</indexterm>
<function>to_regproc</function> ( <type>text</type> )
<returnvalue>regproc</returnvalue>
</para>
<para>
Translates a textual function or procedure name to its OID. A similar result is
obtained by casting the string to type <type>regproc</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found or is ambiguous.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regprocedure</primary>
</indexterm>
<function>to_regprocedure</function> ( <type>text</type> )
<returnvalue>regprocedure</returnvalue>
</para>
<para>
Translates a textual function or procedure name (with argument types) to its OID. A similar result is
obtained by casting the string to type <type>regprocedure</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regrole</primary>
</indexterm>
<function>to_regrole</function> ( <type>text</type> )
<returnvalue>regrole</returnvalue>
</para>
<para>
Translates a textual role name to its OID. A similar result is
obtained by casting the string to type <type>regrole</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found.
</para></entry>
</row>
<row>
<entry id="to-regtype" xreflabel="to_regtype" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regtype</primary>
</indexterm>
<function>to_regtype</function> ( <type>text</type> )
<returnvalue>regtype</returnvalue>
</para>
<para>
Parses a string of text, extracts a potential type name from it,
and translates that name into a type OID. A syntax error in the
string will result in an error; but if the string is a
syntactically valid type name that happens not to be found in the
catalogs, the result is <literal>NULL</literal>. A similar result
is obtained by casting the string to type <type>regtype</type>
(see <xref linkend="datatype-oid"/>), except that that will throw
error for name not found.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regtypemod</primary>
</indexterm>
<function>to_regtypemod</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Parses a string of text, extracts a potential type name from it,
and translates its type modifier, if any. A syntax error in the
string will result in an error; but if the string is a
syntactically valid type name that happens not to be found in the
catalogs, the result is <literal>NULL</literal>. The result is
<literal>-1</literal> if no type modifier is present.
</para>
<para>
<function>to_regtypemod</function> can be combined with
<xref linkend="to-regtype"/> to produce appropriate inputs for
<xref linkend="format-type"/>, allowing a string representing a
type name to be canonicalized.
</para>
<para>
<literal>format_type(to_regtype('varchar(32)'), to_regtypemod('varchar(32)'))</literal>
<returnvalue>character varying(32)</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Most of the functions that reconstruct (decompile) database objects
have an optional <parameter>pretty</parameter> flag, which
if <literal>true</literal> causes the result to
be <quote>pretty-printed</quote>. Pretty-printing suppresses unnecessary
parentheses and adds whitespace for legibility.
The pretty-printed format is more readable, but the default format
is more likely to be interpreted the same way by future versions of
<productname>PostgreSQL</productname>; so avoid using pretty-printed output
for dump purposes. Passing <literal>false</literal> for
the <parameter>pretty</parameter> parameter yields the same result as
omitting the parameter.
</para>
<table id="functions-info-index-column-props">
<title>Index Column Properties</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="1*"/>
<colspec colname="col2" colwidth="3*"/>
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>asc</literal></entry>
<entry>Does the column sort in ascending order on a forward scan?
</entry>
</row>
<row>
<entry><literal>desc</literal></entry>
<entry>Does the column sort in descending order on a forward scan?
</entry>
</row>
<row>
<entry><literal>nulls_first</literal></entry>
<entry>Does the column sort with nulls first on a forward scan?
</entry>
</row>
<row>
<entry><literal>nulls_last</literal></entry>
<entry>Does the column sort with nulls last on a forward scan?
</entry>
</row>
<row>
<entry><literal>orderable</literal></entry>
<entry>Does the column possess any defined sort ordering?
</entry>
</row>
<row>
<entry><literal>distance_orderable</literal></entry>
<entry>Can the column be scanned in order by a <quote>distance</quote>
operator, for example <literal>ORDER BY col &lt;-&gt; constant</literal> ?
</entry>
</row>
<row>
<entry><literal>returnable</literal></entry>
<entry>Can the column value be returned by an index-only scan?
</entry>
</row>
<row>
<entry><literal>search_array</literal></entry>
<entry>Does the column natively support <literal>col = ANY(array)</literal>
searches?
</entry>
</row>
<row>
<entry><literal>search_nulls</literal></entry>
<entry>Does the column support <literal>IS NULL</literal> and
<literal>IS NOT NULL</literal> searches?
</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-info-index-props">
<title>Index Properties</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="1*"/>
<colspec colname="col2" colwidth="3*"/>
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>clusterable</literal></entry>
<entry>Can the index be used in a <literal>CLUSTER</literal> command?
</entry>
</row>
<row>
<entry><literal>index_scan</literal></entry>
<entry>Does the index support plain (non-bitmap) scans?
</entry>
</row>
<row>
<entry><literal>bitmap_scan</literal></entry>
<entry>Does the index support bitmap scans?
</entry>
</row>
<row>
<entry><literal>backward_scan</literal></entry>
<entry>Can the scan direction be changed in mid-scan (to
support <literal>FETCH BACKWARD</literal> on a cursor without
needing materialization)?
</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-info-indexam-props">
<title>Index Access Method Properties</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="1*"/>
<colspec colname="col2" colwidth="3*"/>
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>can_order</literal></entry>
<entry>Does the access method support <literal>ASC</literal>,
<literal>DESC</literal> and related keywords in
<literal>CREATE INDEX</literal>?
</entry>
</row>
<row>
<entry><literal>can_unique</literal></entry>
<entry>Does the access method support unique indexes?
</entry>
</row>
<row>
<entry><literal>can_multi_col</literal></entry>
<entry>Does the access method support indexes with multiple columns?
</entry>
</row>
<row>
<entry><literal>can_exclude</literal></entry>
<entry>Does the access method support exclusion constraints?
</entry>
</row>
<row>
<entry><literal>can_include</literal></entry>
<entry>Does the access method support the <literal>INCLUDE</literal>
clause of <literal>CREATE INDEX</literal>?
</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-settings-flags">
<title>GUC Flags</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="1*"/>
<colspec colname="col2" colwidth="3*"/>
<thead>
<row><entry>Flag</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>EXPLAIN</literal></entry>
<entry>Parameters with this flag are included in
<command>EXPLAIN (SETTINGS)</command> commands.
</entry>
</row>
<row>
<entry><literal>NO_SHOW_ALL</literal></entry>
<entry>Parameters with this flag are excluded from
<command>SHOW ALL</command> commands.
</entry>
</row>
<row>
<entry><literal>NO_RESET</literal></entry>
<entry>Parameters with this flag do not support
<command>RESET</command> commands.
</entry>
</row>
<row>
<entry><literal>NO_RESET_ALL</literal></entry>
<entry>Parameters with this flag are excluded from
<command>RESET ALL</command> commands.
</entry>
</row>
<row>
<entry><literal>NOT_IN_SAMPLE</literal></entry>
<entry>Parameters with this flag are not included in
<filename>postgresql.conf</filename> by default.
</entry>
</row>
<row>
<entry><literal>RUNTIME_COMPUTED</literal></entry>
<entry>Parameters with this flag are runtime-computed ones.
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-object">
<title>Object Information and Addressing Functions</title>
<para>
<xref linkend="functions-info-object-table"/> lists functions related to
database object identification and addressing.
</para>
<table id="functions-info-object-table">
<title>Object Information and Addressing Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_acl</primary>
</indexterm>
<function>pg_get_acl</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>aclitem[]</returnvalue>
</para>
<para>
Returns the <acronym>ACL</acronym> for a database object, specified
by catalog OID, object OID and sub-object ID. This function returns
<literal>NULL</literal> values for undefined objects.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_describe_object</primary>
</indexterm>
<function>pg_describe_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns a textual description of a database object identified by
catalog OID, object OID, and sub-object ID (such as a column number
within a table; the sub-object ID is zero when referring to a whole
object). This description is intended to be human-readable, and might
be translated, depending on server configuration. This is especially
useful to determine the identity of an object referenced in the
<structname>pg_depend</structname> catalog. This function returns
<literal>NULL</literal> values for undefined objects.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_identify_object</primary>
</indexterm>
<function>pg_identify_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>record</returnvalue>
( <parameter>type</parameter> <type>text</type>,
<parameter>schema</parameter> <type>text</type>,
<parameter>name</parameter> <type>text</type>,
<parameter>identity</parameter> <type>text</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by catalog OID, object OID and sub-object
ID.
This information is intended to be machine-readable, and is never
translated.
<parameter>type</parameter> identifies the type of database object;
<parameter>schema</parameter> is the schema name that the object
belongs in, or <literal>NULL</literal> for object types that do not
belong to schemas;
<parameter>name</parameter> is the name of the object, quoted if
necessary, if the name (along with schema name, if pertinent) is
sufficient to uniquely identify the object,
otherwise <literal>NULL</literal>;
<parameter>identity</parameter> is the complete object identity, with
the precise format depending on object type, and each name within the
format being schema-qualified and quoted as necessary. Undefined
objects are identified with <literal>NULL</literal> values.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_identify_object_as_address</primary>
</indexterm>
<function>pg_identify_object_as_address</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>record</returnvalue>
( <parameter>type</parameter> <type>text</type>,
<parameter>object_names</parameter> <type>text[]</type>,
<parameter>object_args</parameter> <type>text[]</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by catalog OID, object OID and sub-object
ID.
The returned information is independent of the current server, that
is, it could be used to identify an identically named object in
another server.
<parameter>type</parameter> identifies the type of database object;
<parameter>object_names</parameter> and
<parameter>object_args</parameter>
are text arrays that together form a reference to the object.
These three values can be passed
to <function>pg_get_object_address</function> to obtain the internal
address of the object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_object_address</primary>
</indexterm>
<function>pg_get_object_address</function> ( <parameter>type</parameter> <type>text</type>, <parameter>object_names</parameter> <type>text[]</type>, <parameter>object_args</parameter> <type>text[]</type> )
<returnvalue>record</returnvalue>
( <parameter>classid</parameter> <type>oid</type>,
<parameter>objid</parameter> <type>oid</type>,
<parameter>objsubid</parameter> <type>integer</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by a type code and object name and argument
arrays.
The returned values are the ones that would be used in system catalogs
such as <structname>pg_depend</structname>; they can be passed to
other system functions such as <function>pg_describe_object</function>
or <function>pg_identify_object</function>.
<parameter>classid</parameter> is the OID of the system catalog
containing the object;
<parameter>objid</parameter> is the OID of the object itself, and
<parameter>objsubid</parameter> is the sub-object ID, or zero if none.
This function is the inverse
of <function>pg_identify_object_as_address</function>.
Undefined objects are identified with <literal>NULL</literal> values.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_get_acl</function> is useful for retrieving and inspecting
the privileges associated with database objects without looking at
specific catalogs. For example, to retrieve all the granted privileges
on objects in the current database:
<programlisting>
postgres=# SELECT
(pg_identify_object(s.classid,s.objid,s.objsubid)).*,
pg_catalog.pg_get_acl(s.classid,s.objid,s.objsubid) AS acl
FROM pg_catalog.pg_shdepend AS s
JOIN pg_catalog.pg_database AS d
ON d.datname = current_database() AND
d.oid = s.dbid
JOIN pg_catalog.pg_authid AS a
ON a.oid = s.refobjid AND
s.refclassid = 'pg_authid'::regclass
WHERE s.deptype = 'a';
-[ RECORD 1 ]-----------------------------------------
type | table
schema | public
name | testtab
identity | public.testtab
acl | {postgres=arwdDxtm/postgres,foo=r/postgres}
</programlisting>
</para>
</sect2>
<sect2 id="functions-info-comment">
<title>Comment Information Functions</title>
<indexterm>
<primary>comment</primary>
<secondary sortas="database objects">about database objects</secondary>
</indexterm>
<para>
The functions shown in <xref linkend="functions-info-comment-table"/>
extract comments previously stored with the <xref linkend="sql-comment"/>
command. A null value is returned if no
comment could be found for the specified parameters.
</para>
<table id="functions-info-comment-table">
<title>Comment Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>col_description</primary>
</indexterm>
<function>col_description</function> ( <parameter>table</parameter> <type>oid</type>, <parameter>column</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a table column, which is specified by the OID
of its table and its column number.
(<function>obj_description</function> cannot be used for table
columns, since columns do not have OIDs of their own.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>obj_description</primary>
</indexterm>
<function>obj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a database object specified by its OID and the
name of the containing system catalog. For
example, <literal>obj_description(123456, 'pg_class')</literal> would
retrieve the comment for the table with OID 123456.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>obj_description</function> ( <parameter>object</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a database object specified by its OID alone.
This is <emphasis>deprecated</emphasis> since there is no guarantee
that OIDs are unique across different system catalogs; therefore, the
wrong comment might be returned.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>shobj_description</primary>
</indexterm>
<function>shobj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a shared database object specified by its OID
and the name of the containing system catalog. This is just
like <function>obj_description</function> except that it is used for
retrieving comments on shared objects (that is, databases, roles, and
tablespaces). Some system catalogs are global to all databases within
each cluster, and the descriptions for objects in them are stored
globally as well.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-validity">
<title>Data Validity Checking Functions</title>
<para>
The functions shown in <xref linkend="functions-info-validity-table"/>
can be helpful for checking validity of proposed input data.
</para>
<table id="functions-info-validity-table">
<title>Data Validity Checking Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_input_is_valid</primary>
</indexterm>
<function>pg_input_is_valid</function> (
<parameter>string</parameter> <type>text</type>,
<parameter>type</parameter> <type>text</type>
)
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether the given <parameter>string</parameter> is valid
input for the specified data type, returning true or false.
</para>
<para>
This function will only work as desired if the data type's input
function has been updated to report invalid input as
a <quote>soft</quote> error. Otherwise, invalid input will abort
the transaction, just as if the string had been cast to the type
directly.
</para>
<para>
<literal>pg_input_is_valid('42', 'integer')</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>pg_input_is_valid('42000000000', 'integer')</literal>
<returnvalue>f</returnvalue>
</para>
<para>
<literal>pg_input_is_valid('1234.567', 'numeric(7,4)')</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_input_error_info</primary>
</indexterm>
<function>pg_input_error_info</function> (
<parameter>string</parameter> <type>text</type>,
<parameter>type</parameter> <type>text</type>
)
<returnvalue>record</returnvalue>
( <parameter>message</parameter> <type>text</type>,
<parameter>detail</parameter> <type>text</type>,
<parameter>hint</parameter> <type>text</type>,
<parameter>sql_error_code</parameter> <type>text</type> )
</para>
<para>
Tests whether the given <parameter>string</parameter> is valid
input for the specified data type; if not, return the details of
the error that would have been thrown. If the input is valid, the
results are NULL. The inputs are the same as
for <function>pg_input_is_valid</function>.
</para>
<para>
This function will only work as desired if the data type's input
function has been updated to report invalid input as
a <quote>soft</quote> error. Otherwise, invalid input will abort
the transaction, just as if the string had been cast to the type
directly.
</para>
<para>
<literal>SELECT * FROM pg_input_error_info('42000000000', 'integer')</literal>
<returnvalue></returnvalue>
<programlisting>
message | detail | hint | sql_error_code
------------------------------------------------------+--------+------+----------------
value "42000000000" is out of range for type integer | | | 22003
</programlisting>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-snapshot">
<title>Transaction ID and Snapshot Information Functions</title>
<para>
The functions shown in <xref linkend="functions-pg-snapshot"/>
provide server transaction information in an exportable form. The main
use of these functions is to determine which transactions were committed
between two snapshots.
</para>
<table id="functions-pg-snapshot">
<title>Transaction ID and Snapshot Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>age</primary>
</indexterm>
<function>age</function> ( <type>xid</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of transactions between the supplied
transaction id and the current transaction counter.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>mxid_age</primary>
</indexterm>
<function>mxid_age</function> ( <type>xid</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of multixacts IDs between the supplied
multixact ID and the current multixacts counter.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_xact_id</primary>
</indexterm>
<function>pg_current_xact_id</function> ()
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the current transaction's ID. It will assign a new one if the
current transaction does not have one already (because it has not
performed any database updates); see <xref
linkend="transaction-id"/> for details. If executed in a
subtransaction, this will return the top-level transaction ID;
see <xref linkend="subxacts"/> for details.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_xact_id_if_assigned</primary>
</indexterm>
<function>pg_current_xact_id_if_assigned</function> ()
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the current transaction's ID, or <literal>NULL</literal> if no
ID is assigned yet. (It's best to use this variant if the transaction
might otherwise be read-only, to avoid unnecessary consumption of an
XID.)
If executed in a subtransaction, this will return the top-level
transaction ID.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_status</primary>
</indexterm>
<function>pg_xact_status</function> ( <type>xid8</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reports the commit status of a recent transaction.
The result is one of <literal>in progress</literal>,
<literal>committed</literal>, or <literal>aborted</literal>,
provided that the transaction is recent enough that the system retains
the commit status of that transaction.
If it is old enough that no references to the transaction survive in
the system and the commit status information has been discarded, the
result is <literal>NULL</literal>.
Applications might use this function, for example, to determine
whether their transaction committed or aborted after the application
and database server become disconnected while
a <literal>COMMIT</literal> is in progress.
Note that prepared transactions are reported as <literal>in
progress</literal>; applications must check <link
linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
if they need to determine whether a transaction ID belongs to a
prepared transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_snapshot</primary>
</indexterm>
<function>pg_current_snapshot</function> ()
<returnvalue>pg_snapshot</returnvalue>
</para>
<para>
Returns a current <firstterm>snapshot</firstterm>, a data structure
showing which transaction IDs are now in-progress.
Only top-level transaction IDs are included in the snapshot;
subtransaction IDs are not shown; see <xref linkend="subxacts"/>
for details.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xip</primary>
</indexterm>
<function>pg_snapshot_xip</function> ( <type>pg_snapshot</type> )
<returnvalue>setof xid8</returnvalue>
</para>
<para>
Returns the set of in-progress transaction IDs contained in a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xmax</primary>
</indexterm>
<function>pg_snapshot_xmax</function> ( <type>pg_snapshot</type> )
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the <structfield>xmax</structfield> of a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xmin</primary>
</indexterm>
<function>pg_snapshot_xmin</function> ( <type>pg_snapshot</type> )
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the <structfield>xmin</structfield> of a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_visible_in_snapshot</primary>
</indexterm>
<function>pg_visible_in_snapshot</function> ( <type>xid8</type>, <type>pg_snapshot</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the given transaction ID <firstterm>visible</firstterm> according
to this snapshot (that is, was it completed before the snapshot was
taken)? Note that this function will not give the correct answer for
a subtransaction ID (subxid); see <xref linkend="subxacts"/> for
details.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_multixact_members</primary>
</indexterm>
<function>pg_get_multixact_members</function> ( <parameter>multixid</parameter> <type>xid</type> )
<returnvalue>setof record</returnvalue>
( <parameter>xid</parameter> <type>xid</type>,
<parameter>mode</parameter> <type>text</type> )
</para>
<para>
Returns the transaction ID and lock mode for each member of the
specified multixact ID. The lock modes <literal>forupd</literal>,
<literal>fornokeyupd</literal>, <literal>sh</literal>, and
<literal>keysh</literal> correspond to the row-level locks
<literal>FOR UPDATE</literal>, <literal>FOR NO KEY UPDATE</literal>,
<literal>FOR SHARE</literal>, and <literal>FOR KEY SHARE</literal>,
respectively, as described in <xref linkend="locking-rows"/>. Two
additional modes are specific to multixacts:
<literal>nokeyupd</literal>, used by updates that do not modify key
columns, and <literal>upd</literal>, used by updates or deletes that
modify key columns.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_multixact_stats</primary>
</indexterm>
<function>pg_get_multixact_stats</function> ()
<returnvalue>record</returnvalue>
( <parameter>num_mxids</parameter> <type>integer</type>,
<parameter>num_members</parameter> <type>bigint</type>,
<parameter>members_size</parameter> <type>bigint</type>,
<parameter>oldest_multixact</parameter> <type>xid</type> )
</para>
<para>
Returns statistics about current multixact usage:
<literal>num_mxids</literal> is the total number of multixact IDs
currently present in the system, <literal>num_members</literal> is
the total number of multixact member entries currently present in
the system, <literal>members_size</literal> is the storage occupied
by <literal>num_members</literal> in the
<literal>pg_multixact/members</literal> directory,
<literal>oldest_multixact</literal> is the oldest multixact ID still
in use.
</para>
<para>
The function reports statistics at the time it is invoked. Values may
vary between calls, even within a single transaction.
</para>
<para>
To use this function, you must have privileges of the
<literal>pg_read_all_stats</literal> role.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The internal transaction ID type <type>xid</type> is 32 bits wide and
wraps around every 4 billion transactions. However,
the functions shown in <xref linkend="functions-pg-snapshot"/>, except
<function>age</function>, <function>mxid_age</function>, and
<function>pg_get_multixact_members</function>, use a
64-bit type <type>xid8</type> that does not wrap around during the life
of an installation and can be converted to <type>xid</type> by casting if
required; see <xref linkend="transaction-id"/> for details.
The data type <type>pg_snapshot</type> stores information about
transaction ID visibility at a particular moment in time. Its components
are described in <xref linkend="functions-pg-snapshot-parts"/>.
<type>pg_snapshot</type>'s textual representation is
<literal><replaceable>xmin</replaceable>:<replaceable>xmax</replaceable>:<replaceable>xip_list</replaceable></literal>.
For example <literal>10:20:10,14,15</literal> means
<literal>xmin=10, xmax=20, xip_list=10, 14, 15</literal>.
</para>
<table id="functions-pg-snapshot-parts">
<title>Snapshot Components</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="1*"/>
<colspec colname="col2" colwidth="3*"/>
<thead>
<row>
<entry>Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>xmin</structfield></entry>
<entry>
Lowest transaction ID that was still active. All transaction IDs
less than <structfield>xmin</structfield> are either committed and visible,
or rolled back and dead.
</entry>
</row>
<row>
<entry><structfield>xmax</structfield></entry>
<entry>
One past the highest completed transaction ID. All transaction IDs
greater than or equal to <structfield>xmax</structfield> had not yet
completed as of the time of the snapshot, and thus are invisible.
</entry>
</row>
<row>
<entry><structfield>xip_list</structfield></entry>
<entry>
Transactions in progress at the time of the snapshot. A transaction
ID that is <literal>xmin &lt;= <replaceable>X</replaceable> &lt;
xmax</literal> and not in this list was already completed at the time
of the snapshot, and thus is either visible or dead according to its
commit status. This list does not include the transaction IDs of
subtransactions (subxids).
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In releases of <productname>PostgreSQL</productname> before 13 there was
no <type>xid8</type> type, so variants of these functions were provided
that used <type>bigint</type> to represent a 64-bit XID, with a
correspondingly distinct snapshot data type <type>txid_snapshot</type>.
These older functions have <literal>txid</literal> in their names. They
are still supported for backward compatibility, but may be removed from a
future release. See <xref linkend="functions-txid-snapshot"/>.
</para>
<table id="functions-txid-snapshot">
<title>Deprecated Transaction ID and Snapshot Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current</primary>
</indexterm>
<function>txid_current</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_current_xact_id()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current_if_assigned</primary>
</indexterm>
<function>txid_current_if_assigned</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_current_xact_id_if_assigned()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current_snapshot</primary>
</indexterm>
<function>txid_current_snapshot</function> ()
<returnvalue>txid_snapshot</returnvalue>
</para>
<para>
See <function>pg_current_snapshot()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xip</primary>
</indexterm>
<function>txid_snapshot_xip</function> ( <type>txid_snapshot</type> )
<returnvalue>setof bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xip()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xmax</primary>
</indexterm>
<function>txid_snapshot_xmax</function> ( <type>txid_snapshot</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xmax()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xmin</primary>
</indexterm>
<function>txid_snapshot_xmin</function> ( <type>txid_snapshot</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xmin()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_visible_in_snapshot</primary>
</indexterm>
<function>txid_visible_in_snapshot</function> ( <type>bigint</type>, <type>txid_snapshot</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
See <function>pg_visible_in_snapshot()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_status</primary>
</indexterm>
<function>txid_status</function> ( <type>bigint</type> )
<returnvalue>text</returnvalue>
</para>
<para>
See <function>pg_xact_status()</function>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-commit-timestamp">
<title>Committed Transaction Information Functions</title>
<para>
The functions shown in <xref linkend="functions-commit-timestamp"/>
provide information about when past transactions were committed.
They only provide useful data when the
<xref linkend="guc-track-commit-timestamp"/> configuration option is
enabled, and only for transactions that were committed after it was
enabled. Commit timestamp information is routinely removed during
vacuum.
</para>
<table id="functions-commit-timestamp">
<title>Committed Transaction Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_commit_timestamp</primary>
</indexterm>
<function>pg_xact_commit_timestamp</function> ( <type>xid</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the commit timestamp of a transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_commit_timestamp_origin</primary>
</indexterm>
<function>pg_xact_commit_timestamp_origin</function> ( <type>xid</type> )
<returnvalue>record</returnvalue>
( <parameter>timestamp</parameter> <type>timestamp with time zone</type>,
<parameter>roident</parameter> <type>oid</type>)
</para>
<para>
Returns the commit timestamp and replication origin of a transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_committed_xact</primary>
</indexterm>
<function>pg_last_committed_xact</function> ()
<returnvalue>record</returnvalue>
( <parameter>xid</parameter> <type>xid</type>,
<parameter>timestamp</parameter> <type>timestamp with time zone</type>,
<parameter>roident</parameter> <type>oid</type> )
</para>
<para>
Returns the transaction ID, commit timestamp and replication origin
of the latest committed transaction.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-controldata">
<title>Control Data Functions</title>
<para>
The functions shown in <xref linkend="functions-controldata"/>
print information initialized during <command>initdb</command>, such
as the catalog version. They also show information about write-ahead
logging and checkpoint processing. This information is cluster-wide,
not specific to any one database. These functions provide most of the same
information, from the same source, as the
<xref linkend="app-pgcontroldata"/> application.
</para>
<table id="functions-controldata">
<title>Control Data Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_checkpoint</primary>
</indexterm>
<function>pg_control_checkpoint</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about current checkpoint state, as shown in
<xref linkend="functions-pg-control-checkpoint"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_system</primary>
</indexterm>
<function>pg_control_system</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about current control file state, as shown in
<xref linkend="functions-pg-control-system"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_init</primary>
</indexterm>
<function>pg_control_init</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about cluster initialization state, as shown in
<xref linkend="functions-pg-control-init"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_recovery</primary>
</indexterm>
<function>pg_control_recovery</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about recovery state, as shown in
<xref linkend="functions-pg-control-recovery"/>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-checkpoint">
<title><function>pg_control_checkpoint</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>checkpoint_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>redo_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>redo_wal_file</structfield></entry>
<entry><type>text</type></entry>
</row>
<row>
<entry><structfield>timeline_id</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>prev_timeline_id</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>full_page_writes</structfield></entry>
<entry><type>boolean</type></entry>
</row>
<row>
<entry><structfield>next_xid</structfield></entry>
<entry><type>text</type></entry>
</row>
<row>
<entry><structfield>next_oid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>next_multixact_id</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>next_multi_offset</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_xid_dbid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>oldest_active_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_multi_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_multi_dbid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>oldest_commit_ts_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>newest_commit_ts_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>checkpoint_time</structfield></entry>
<entry><type>timestamp with time zone</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-system">
<title><function>pg_control_system</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>pg_control_version</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>catalog_version_no</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>system_identifier</structfield></entry>
<entry><type>bigint</type></entry>
</row>
<row>
<entry><structfield>pg_control_last_modified</structfield></entry>
<entry><type>timestamp with time zone</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-init">
<title><function>pg_control_init</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>max_data_alignment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>database_block_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>blocks_per_segment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>wal_block_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>bytes_per_wal_segment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_identifier_length</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_index_columns</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_toast_chunk_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>large_object_chunk_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>float8_pass_by_value</structfield></entry>
<entry><type>boolean</type></entry>
</row>
<row>
<entry><structfield>data_page_checksum_version</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>default_char_signedness</structfield></entry>
<entry><type>boolean</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-recovery">
<title><function>pg_control_recovery</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>min_recovery_end_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>min_recovery_end_timeline</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>backup_start_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>backup_end_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>end_of_backup_record_required</structfield></entry>
<entry><type>boolean</type></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-version">
<title>Version Information Functions</title>
<para>
The functions shown in <xref linkend="functions-version"/>
print version information.
</para>
<table id="functions-version">
<title>Version Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>version</primary>
</indexterm>
<function>version</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns a string describing the <productname>PostgreSQL</productname>
server's version. You can also get this information from
<xref linkend="guc-server-version"/>, or for a machine-readable
version use <xref linkend="guc-server-version-num"/>. Software
developers should use <varname>server_version_num</varname> (available
since 8.2) or <xref linkend="libpq-PQserverVersion"/> instead of
parsing the text version.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>unicode_version</primary>
</indexterm>
<function>unicode_version</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns a string representing the version of Unicode used by
<productname>PostgreSQL</productname>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>icu_unicode_version</primary>
</indexterm>
<function>icu_unicode_version</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns a string representing the version of Unicode used by ICU, if
the server was built with ICU support; otherwise returns
<literal>NULL</literal> </para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-info-wal-summary">
<title>WAL Summarization Information Functions</title>
<para>
The functions shown in <xref linkend="functions-wal-summary"/>
print information about the status of WAL summarization.
See <xref linkend="guc-summarize-wal" />.
</para>
<table id="functions-wal-summary">
<title>WAL Summarization Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_available_wal_summaries</primary>
</indexterm>
<function>pg_available_wal_summaries</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>tli</parameter> <type>bigint</type>,
<parameter>start_lsn</parameter> <type>pg_lsn</type>,
<parameter>end_lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Returns information about the WAL summary files present in the
data directory, under <literal>pg_wal/summaries</literal>.
One row will be returned per WAL summary file. Each file summarizes
WAL on the indicated TLI within the indicated LSN range. This function
might be useful to determine whether enough WAL summaries are present
on the server to take an incremental backup based on some prior
backup whose start LSN is known.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_summary_contents</primary>
</indexterm>
<function>pg_wal_summary_contents</function> ( <parameter>tli</parameter> <type>bigint</type>, <parameter>start_lsn</parameter> <type>pg_lsn</type>, <parameter>end_lsn</parameter> <type>pg_lsn</type> )
<returnvalue>setof record</returnvalue>
( <parameter>relfilenode</parameter> <type>oid</type>,
<parameter>reltablespace</parameter> <type>oid</type>,
<parameter>reldatabase</parameter> <type>oid</type>,
<parameter>relforknumber</parameter> <type>smallint</type>,
<parameter>relblocknumber</parameter> <type>bigint</type>,
<parameter>is_limit_block</parameter> <type>boolean</type> )
</para>
<para>
Returns one information about the contents of a single WAL summary file
identified by TLI and starting and ending LSNs. Each row with
<literal>is_limit_block</literal> false indicates that the block
identified by the remaining output columns was modified by at least
one WAL record within the range of records summarized by this file.
Each row with <literal>is_limit_block</literal> true indicates either
that (a) the relation fork was truncated to the length given by
<literal>relblocknumber</literal> within the relevant range of WAL
records or (b) that the relation fork was created or dropped within
the relevant range of WAL records; in such cases,
<literal>relblocknumber</literal> will be zero.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_wal_summarizer_state</primary>
</indexterm>
<function>pg_get_wal_summarizer_state</function> ()
<returnvalue>record</returnvalue>
( <parameter>summarized_tli</parameter> <type>bigint</type>,
<parameter>summarized_lsn</parameter> <type>pg_lsn</type>,
<parameter>pending_lsn</parameter> <type>pg_lsn</type>,
<parameter>summarizer_pid</parameter> <type>int</type> )
</para>
<para>
Returns information about the progress of the WAL summarizer. If the
WAL summarizer has never run since the instance was started, then
<literal>summarized_tli</literal> and <literal>summarized_lsn</literal>
will be <literal>0</literal> and <literal>0/00000000</literal> respectively;
otherwise, they will be the TLI and ending LSN of the last WAL summary
file written to disk. If the WAL summarizer is currently running,
<literal>pending_lsn</literal> will be the ending LSN of the last
record that it has consumed, which must always be greater than or
equal to <literal>summarized_lsn</literal>; if the WAL summarizer is
not running, it will be equal to <literal>summarized_lsn</literal>.
<literal>summarizer_pid</literal> is the PID of the WAL summarizer
process, if it is running, and otherwise NULL.
</para>
<para>
As a special exception, the WAL summarizer will refuse to generate
WAL summary files if run on WAL generated under
<literal>wal_level=minimal</literal>, since such summaries would be
unsafe to use as the basis for an incremental backup. In this case,
the fields above will continue to advance as if summaries were being
generated, but nothing will be written to disk. Once the summarizer
reaches WAL generated while <literal>wal_level</literal> was set
to <literal>replica</literal> or higher, it will resume writing
summaries to disk.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
</sect1>
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