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9.27. System Information Functions and Operators #

   9.27.1. Session Information Functions
   9.27.2. Access Privilege Inquiry Functions
   9.27.3. Schema Visibility Inquiry Functions
   9.27.4. System Catalog Information Functions
   9.27.5. Object Information and Addressing Functions
   9.27.6. Comment Information Functions
   9.27.7. Data Validity Checking Functions
   9.27.8. Transaction ID and Snapshot Information Functions
   9.27.9. Committed Transaction Information Functions
   9.27.10. Control Data Functions
   9.27.11. Version Information Functions
   9.27.12. WAL Summarization Information Functions

   The functions described in this section are used to obtain various
   information about a PostgreSQL installation.

9.27.1. Session Information Functions #

   Table 9.71 shows several functions that extract session and system
   information.

   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 Section 27.2.26 for more information.

   Table 9.71. Session Information Functions

   Function

   Description

   current_catalog → name

   current_database () → name

   Returns the name of the current database. (Databases are called
   “catalogs” in the SQL standard, so current_catalog is the standard's
   spelling.)

   current_query () → text

   Returns the text of the currently executing query, as submitted by the
   client (which might contain more than one statement).

   current_role → name

   This is equivalent to current_user.

   current_schema → name

   current_schema () → name

   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.

   current_schemas ( include_implicit boolean ) → name[]

   Returns an array of the names of all schemas presently in the effective
   search path, in their priority order. (Items in the current search_path
   setting that do not correspond to existing, searchable schemas are
   omitted.) If the Boolean argument is true, then implicitly-searched
   system schemas such as pg_catalog are included in the result.

   current_user → name

   Returns the user name of the current execution context.

   inet_client_addr () → inet

   Returns the IP address of the current client, or NULL if the current
   connection is via a Unix-domain socket.

   inet_client_port () → integer

   Returns the IP port number of the current client, or NULL if the
   current connection is via a Unix-domain socket.

   inet_server_addr () → inet

   Returns the IP address on which the server accepted the current
   connection, or NULL if the current connection is via a Unix-domain
   socket.

   inet_server_port () → integer

   Returns the IP port number on which the server accepted the current
   connection, or NULL if the current connection is via a Unix-domain
   socket.

   pg_backend_pid () → integer

   Returns the process ID of the server process attached to the current
   session.

   pg_blocking_pids ( integer ) → integer[]

   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.

   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, pg_backend_pid 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.

   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.

   pg_conf_load_time () → timestamp with time zone

   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.

   pg_current_logfile ( [ text ] ) → text

   Returns the path name of the log file currently in use by the logging
   collector. The path includes the log_directory directory and the
   individual log file name. The result is NULL if the logging collector
   is disabled. When multiple log files exist, each in a different format,
   pg_current_logfile without an argument returns the path of the file
   having the first format found in the ordered list: stderr, csvlog,
   jsonlog. NULL is returned if no log file has any of these formats. To
   request information about a specific log file format, supply either
   csvlog, jsonlog or stderr as the value of the optional parameter. The
   result is NULL if the log format requested is not configured in
   log_destination. The result reflects the contents of the
   current_logfiles file.

   This function is restricted to superusers and roles with privileges of
   the pg_monitor role by default, but other users can be granted EXECUTE
   to run the function.

   pg_get_loaded_modules () → setof record ( module_name text, version
   text, file_name text )

   Returns a list of the loadable modules that are loaded into the current
   server session. The module_name and version fields are NULL unless the
   module author supplied values for them using the PG_MODULE_MAGIC_EXT
   macro. The file_name field gives the file name of the module (shared
   library).

   pg_my_temp_schema () → oid

   Returns the OID of the current session's temporary schema, or zero if
   it has none (because it has not created any temporary tables).

   pg_is_other_temp_schema ( oid ) → boolean

   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.)

   pg_jit_available () → boolean

   Returns true if a JIT compiler extension is available (see Chapter 30)
   and the jit configuration parameter is set to on.

   pg_numa_available () → boolean

   Returns true if the server has been compiled with NUMA support.

   pg_listening_channels () → setof text

   Returns the set of names of asynchronous notification channels that the
   current session is listening to.

   pg_notification_queue_usage () → double precision

   Returns the fraction (0–1) of the asynchronous notification queue's
   maximum size that is currently occupied by notifications that are
   waiting to be processed. See LISTEN and NOTIFY for more information.

   pg_postmaster_start_time () → timestamp with time zone

   Returns the time when the server started.

   pg_safe_snapshot_blocking_pids ( integer ) → integer[]

   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.

   A session running a SERIALIZABLE transaction blocks a SERIALIZABLE READ
   ONLY DEFERRABLE transaction from acquiring a snapshot until the latter
   determines that it is safe to avoid taking any predicate locks. See
   Section 13.2.3 for more information about serializable and deferrable
   transactions.

   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.

   pg_trigger_depth () → integer

   Returns the current nesting level of PostgreSQL triggers (0 if not
   called, directly or indirectly, from inside a trigger).

   session_user → name

   Returns the session user's name.

   system_user → text

   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 auth_method:identity or
   NULL if the user has not been authenticated (for example if Trust
   authentication has been used).

   user → name

   This is equivalent to current_user.

Note

   current_catalog, current_role, current_schema, current_user,
   session_user, and user have special syntactic status in SQL: they must
   be called without trailing parentheses. In PostgreSQL, parentheses can
   optionally be used with current_schema, but not with the others.

   The session_user is normally the user who initiated the current
   database connection; but superusers can change this setting with SET
   SESSION AUTHORIZATION. The current_user is the user identifier that is
   applicable for permission checking. Normally it is equal to the session
   user, but it can be changed with SET ROLE. It also changes during the
   execution of functions with the attribute SECURITY DEFINER. In Unix
   parlance, the session user is the “real user” and the current user is
   the “effective user”. current_role and user are synonyms for
   current_user. (The SQL standard draws a distinction between
   current_role and current_user, but PostgreSQL does not, since it
   unifies users and roles into a single kind of entity.)

9.27.2. Access Privilege Inquiry Functions #

   Table 9.72 lists functions that allow querying object access privileges
   programmatically. (See Section 5.8 for more information about
   privileges.) In these functions, the user whose privileges are being
   inquired about can be specified by name or by OID (pg_authid.oid), or
   if the name is given as public then the privileges of the PUBLIC
   pseudo-role are checked. Also, the user argument can be omitted
   entirely, in which case the current_user 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., SELECT). Optionally, WITH GRANT OPTION 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:
SELECT has_table_privilege('myschema.mytable', 'select');
SELECT has_table_privilege('joe', 'mytable', 'INSERT, SELECT WITH GRANT OPTION')
;

   Table 9.72. Access Privilege Inquiry Functions

   Function

   Description

   has_any_column_privilege ( [ user name or oid, ] table text or oid,
   privilege text ) → boolean

   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 SELECT, INSERT, UPDATE, and REFERENCES.

   has_column_privilege ( [ user name or oid, ] table text or oid, column
   text or smallint, privilege text ) → boolean

   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 (pg_attribute.attnum).
   Allowable privilege types are SELECT, INSERT, UPDATE, and REFERENCES.

   has_database_privilege ( [ user name or oid, ] database text or oid,
   privilege text ) → boolean

   Does user have privilege for database? Allowable privilege types are
   CREATE, CONNECT, TEMPORARY, and TEMP (which is equivalent to
   TEMPORARY).

   has_foreign_data_wrapper_privilege ( [ user name or oid, ] fdw text or
   oid, privilege text ) → boolean

   Does user have privilege for foreign-data wrapper? The only allowable
   privilege type is USAGE.

   has_function_privilege ( [ user name or oid, ] function text or oid,
   privilege text ) → boolean

   Does user have privilege for function? The only allowable privilege
   type is EXECUTE.

   When specifying a function by name rather than by OID, the allowed
   input is the same as for the regprocedure data type (see Section 8.19).
   An example is:
SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');

   has_language_privilege ( [ user name or oid, ] language text or oid,
   privilege text ) → boolean

   Does user have privilege for language? The only allowable privilege
   type is USAGE.

   has_largeobject_privilege ( [ user name or oid, ] largeobject oid,
   privilege text ) → boolean

   Does user have privilege for large object? Allowable privilege types
   are SELECT and UPDATE.

   has_parameter_privilege ( [ user name or oid, ] parameter text,
   privilege text ) → boolean

   Does user have privilege for configuration parameter? The parameter
   name is case-insensitive. Allowable privilege types are SET and ALTER
   SYSTEM.

   has_schema_privilege ( [ user name or oid, ] schema text or oid,
   privilege text ) → boolean

   Does user have privilege for schema? Allowable privilege types are
   CREATE and USAGE.

   has_sequence_privilege ( [ user name or oid, ] sequence text or oid,
   privilege text ) → boolean

   Does user have privilege for sequence? Allowable privilege types are
   USAGE, SELECT, and UPDATE.

   has_server_privilege ( [ user name or oid, ] server text or oid,
   privilege text ) → boolean

   Does user have privilege for foreign server? The only allowable
   privilege type is USAGE.

   has_table_privilege ( [ user name or oid, ] table text or oid,
   privilege text ) → boolean

   Does user have privilege for table? Allowable privilege types are
   SELECT, INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, TRIGGER, and
   MAINTAIN.

   has_tablespace_privilege ( [ user name or oid, ] tablespace text or
   oid, privilege text ) → boolean

   Does user have privilege for tablespace? The only allowable privilege
   type is CREATE.

   has_type_privilege ( [ user name or oid, ] type text or oid, privilege
   text ) → boolean

   Does user have privilege for data type? The only allowable privilege
   type is USAGE. When specifying a type by name rather than by OID, the
   allowed input is the same as for the regtype data type (see
   Section 8.19).

   pg_has_role ( [ user name or oid, ] role text or oid, privilege text )
   → boolean

   Does user have privilege for role? Allowable privilege types are
   MEMBER, USAGE, and SET. MEMBER denotes direct or indirect membership in
   the role without regard to what specific privileges may be conferred.
   USAGE denotes whether the privileges of the role are immediately
   available without doing SET ROLE, while SET denotes whether it is
   possible to change to the role using the SET ROLE command. WITH ADMIN
   OPTION or WITH GRANT OPTION can be added to any of these privilege
   types to test whether the ADMIN privilege is held (all six spellings
   test the same thing). This function does not allow the special case of
   setting user to public, because the PUBLIC pseudo-role can never be a
   member of real roles.

   row_security_active ( table text or oid ) → boolean

   Is row-level security active for the specified table in the context of
   the current user and current environment?

   Table 9.73 shows the operators available for the aclitem type, which is
   the catalog representation of access privileges. See Section 5.8 for
   information about how to read access privilege values.

   Table 9.73. aclitem Operators

   Operator

   Description

   Example(s)

   aclitem = aclitem → boolean

   Are aclitems equal? (Notice that type aclitem lacks the usual set of
   comparison operators; it has only equality. In turn, aclitem arrays can
   only be compared for equality.)

   'calvin=r*w/hobbes'::aclitem = 'calvin=r*w*/hobbes'::aclitem → f

   aclitem[] @> aclitem → boolean

   Does array contain the specified privileges? (This is true if there is
   an array entry that matches the aclitem's grantee and grantor, and has
   at least the specified set of privileges.)

   '{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] @>
   'calvin=r*/hobbes'::aclitem → t

   aclitem[] ~ aclitem → boolean

   This is a deprecated alias for @>.

   '{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] ~
   'calvin=r*/hobbes'::aclitem → t

   Table 9.74 shows some additional functions to manage the aclitem type.

   Table 9.74. aclitem Functions

   Function

   Description

   acldefault ( type "char", ownerId oid ) → aclitem[]

   Constructs an aclitem array holding the default access privileges for
   an object of type type belonging to the role with OID ownerId. This
   represents the access privileges that will be assumed when an object's
   ACL entry is null. (The default access privileges are described in
   Section 5.8.) The type parameter must be one of 'c' for COLUMN, 'r' for
   TABLE and table-like objects, 's' for SEQUENCE, 'd' for DATABASE, 'f'
   for FUNCTION or PROCEDURE, 'l' for LANGUAGE, 'L' for LARGE OBJECT, 'n'
   for SCHEMA, 'p' for PARAMETER, 't' for TABLESPACE, 'F' for FOREIGN DATA
   WRAPPER, 'S' for FOREIGN SERVER, or 'T' for TYPE or DOMAIN.

   aclexplode ( aclitem[] ) → setof record ( grantor oid, grantee oid,
   privilege_type text, is_grantable boolean )

   Returns the aclitem array as a set of rows. If the grantee is the
   pseudo-role PUBLIC, it is represented by zero in the grantee column.
   Each granted privilege is represented as SELECT, INSERT, etc (see
   Table 5.1 for a full list). Note that each privilege is broken out as a
   separate row, so only one keyword appears in the privilege_type column.

   makeaclitem ( grantee oid, grantor oid, privileges text, is_grantable
   boolean ) → aclitem

   Constructs an aclitem with the given properties. privileges is a
   comma-separated list of privilege names such as SELECT, INSERT, 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.)

9.27.3. Schema Visibility Inquiry Functions #

   Table 9.75 shows functions that determine whether a certain object is
   visible 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:
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);

   For functions and operators, an object in the search path is said to be
   visible if there is no object of the same name and argument data
   type(s) earlier in the path. For operator classes and families, both
   the name and the associated index access method are considered.

   Table 9.75. Schema Visibility Inquiry Functions

   Function

   Description

   pg_collation_is_visible ( collation oid ) → boolean

   Is collation visible in search path?

   pg_conversion_is_visible ( conversion oid ) → boolean

   Is conversion visible in search path?

   pg_function_is_visible ( function oid ) → boolean

   Is function visible in search path? (This also works for procedures and
   aggregates.)

   pg_opclass_is_visible ( opclass oid ) → boolean

   Is operator class visible in search path?

   pg_operator_is_visible ( operator oid ) → boolean

   Is operator visible in search path?

   pg_opfamily_is_visible ( opclass oid ) → boolean

   Is operator family visible in search path?

   pg_statistics_obj_is_visible ( stat oid ) → boolean

   Is statistics object visible in search path?

   pg_table_is_visible ( table oid ) → boolean

   Is table visible in search path? (This works for all types of
   relations, including views, materialized views, indexes, sequences and
   foreign tables.)

   pg_ts_config_is_visible ( config oid ) → boolean

   Is text search configuration visible in search path?

   pg_ts_dict_is_visible ( dict oid ) → boolean

   Is text search dictionary visible in search path?

   pg_ts_parser_is_visible ( parser oid ) → boolean

   Is text search parser visible in search path?

   pg_ts_template_is_visible ( template oid ) → boolean

   Is text search template visible in search path?

   pg_type_is_visible ( type oid ) → boolean

   Is type (or domain) visible in search path?

   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 (regclass, regtype, regprocedure, regoperator,
   regconfig, or regdictionary), for example:
SELECT pg_type_is_visible('myschema.widget'::regtype);

   Note that it would not make much sense to test a non-schema-qualified
   type name in this way — if the name can be recognized at all, it must
   be visible.

9.27.4. System Catalog Information Functions #

   Table 9.76 lists functions that extract information from the system
   catalogs.

   Table 9.76. System Catalog Information Functions

   Function

   Description

   format_type ( type oid, typemod integer ) → text

   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.

   pg_basetype ( regtype ) → regtype

   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.

   Assuming CREATE DOMAIN mytext AS text:

   pg_basetype('mytext'::regtype) → text

   pg_char_to_encoding ( encoding name ) → integer

   Converts the supplied encoding name into an integer representing the
   internal identifier used in some system catalog tables. Returns -1 if
   an unknown encoding name is provided.

   pg_encoding_to_char ( encoding integer ) → name

   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.

   pg_get_catalog_foreign_keys () → setof record ( fktable regclass,
   fkcols text[], pktable regclass, pkcols text[], is_array boolean,
   is_opt boolean )

   Returns a set of records describing the foreign key relationships that
   exist within the PostgreSQL system catalogs. The fktable column
   contains the name of the referencing catalog, and the fkcols column
   contains the name(s) of the referencing column(s). Similarly, the
   pktable column contains the name of the referenced catalog, and the
   pkcols column contains the name(s) of the referenced column(s). If
   is_array is true, the last referencing column is an array, each of
   whose elements should match some entry in the referenced catalog. If
   is_opt is true, the referencing column(s) are allowed to contain zeroes
   instead of a valid reference.

   pg_get_constraintdef ( constraint oid [, pretty boolean ] ) → text

   Reconstructs the creating command for a constraint. (This is a
   decompiled reconstruction, not the original text of the command.)

   pg_get_expr ( expr pg_node_tree, relation oid [, pretty boolean ] ) →
   text

   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.

   pg_get_functiondef ( func oid ) → text

   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 CREATE OR REPLACE FUNCTION or CREATE OR REPLACE
   PROCEDURE statement.

   pg_get_function_arguments ( func oid ) → text

   Reconstructs the argument list of a function or procedure, in the form
   it would need to appear in within CREATE FUNCTION (including default
   values).

   pg_get_function_identity_arguments ( func oid ) → text

   Reconstructs the argument list necessary to identify a function or
   procedure, in the form it would need to appear in within commands such
   as ALTER FUNCTION. This form omits default values.

   pg_get_function_result ( func oid ) → text

   Reconstructs the RETURNS clause of a function, in the form it would
   need to appear in within CREATE FUNCTION. Returns NULL for a procedure.

   pg_get_indexdef ( index oid [, column integer, pretty boolean ] ) →
   text

   Reconstructs the creating command for an index. (This is a decompiled
   reconstruction, not the original text of the command.) If column is
   supplied and is not zero, only the definition of that column is
   reconstructed.

   pg_get_keywords () → setof record ( word text, catcode "char",
   barelabel boolean, catdesc text, baredesc text )

   Returns a set of records describing the SQL keywords recognized by the
   server. The word column contains the keyword. The catcode column
   contains a category code: U for an unreserved keyword, C for a keyword
   that can be a column name, T for a keyword that can be a type or
   function name, or R for a fully reserved keyword. The barelabel column
   contains true if the keyword can be used as a “bare” column label in
   SELECT lists, or false if it can only be used after AS. The catdesc
   column contains a possibly-localized string describing the keyword's
   category. The baredesc column contains a possibly-localized string
   describing the keyword's column label status.

   pg_get_partkeydef ( table oid ) → text

   Reconstructs the definition of a partitioned table's partition key, in
   the form it would have in the PARTITION BY clause of CREATE TABLE.
   (This is a decompiled reconstruction, not the original text of the
   command.)

   pg_get_ruledef ( rule oid [, pretty boolean ] ) → text

   Reconstructs the creating command for a rule. (This is a decompiled
   reconstruction, not the original text of the command.)

   pg_get_serial_sequence ( table text, column text ) → text

   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 (serial,
   smallserial, bigserial), it is the sequence created for that serial
   column definition. In the latter case, the association can be modified
   or removed with ALTER SEQUENCE OWNED BY. (This function probably should
   have been called pg_get_owned_sequence; 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
   Section 9.17).

   A typical use is in reading the current value of the sequence for an
   identity or serial column, for example:
SELECT currval(pg_get_serial_sequence('sometable', 'id'));

   pg_get_statisticsobjdef ( statobj oid ) → text

   Reconstructs the creating command for an extended statistics object.
   (This is a decompiled reconstruction, not the original text of the
   command.)

   pg_get_triggerdef ( trigger oid [, pretty boolean ] ) → text

   Reconstructs the creating command for a trigger. (This is a decompiled
   reconstruction, not the original text of the command.)

   pg_get_userbyid ( role oid ) → name

   Returns a role's name given its OID.

   pg_get_viewdef ( view oid [, pretty boolean ] ) → text

   Reconstructs the underlying SELECT command for a view or materialized
   view. (This is a decompiled reconstruction, not the original text of
   the command.)

   pg_get_viewdef ( view oid, wrap_column integer ) → text

   Reconstructs the underlying SELECT 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.

   pg_get_viewdef ( view text [, pretty boolean ] ) → text

   Reconstructs the underlying SELECT 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.)

   pg_index_column_has_property ( index regclass, column integer, property
   text ) → boolean

   Tests whether an index column has the named property. Common index
   column properties are listed in Table 9.77. (Note that extension access
   methods can define additional property names for their indexes.) NULL
   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.

   pg_index_has_property ( index regclass, property text ) → boolean

   Tests whether an index has the named property. Common index properties
   are listed in Table 9.78. (Note that extension access methods can
   define additional property names for their indexes.) NULL 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.

   pg_indexam_has_property ( am oid, property text ) → boolean

   Tests whether an index access method has the named property. Access
   method properties are listed in Table 9.79. NULL 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.

   pg_options_to_table ( options_array text[] ) → setof record (
   option_name text, option_value text )

   Returns the set of storage options represented by a value from
   pg_class.reloptions or pg_attribute.attoptions.

   pg_settings_get_flags ( guc text ) → text[]

   Returns an array of the flags associated with the given GUC, or NULL 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
   Table 9.80 are exposed.

   pg_tablespace_databases ( tablespace oid ) → setof oid

   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 pg_tablespace_databases and query their pg_class
   catalogs.

   pg_tablespace_location ( tablespace oid ) → text

   Returns the file system path that this tablespace is located in.

   pg_typeof ( "any" ) → regtype

   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 regtype, which is an OID
   alias type (see Section 8.19); this means that it is the same as an OID
   for comparison purposes but displays as a type name.

   pg_typeof(33) → integer

   COLLATION FOR ( "any" ) → text

   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 NULL is returned. If the
   argument is not of a collatable data type, then an error is raised.

   collation for ('foo'::text) → "default"

   collation for ('foo' COLLATE "de_DE") → "de_DE"

   to_regclass ( text ) → regclass

   Translates a textual relation name to its OID. A similar result is
   obtained by casting the string to type regclass (see Section 8.19);
   however, this function will return NULL rather than throwing an error
   if the name is not found.

   to_regcollation ( text ) → regcollation

   Translates a textual collation name to its OID. A similar result is
   obtained by casting the string to type regcollation (see Section 8.19);
   however, this function will return NULL rather than throwing an error
   if the name is not found.

   to_regnamespace ( text ) → regnamespace

   Translates a textual schema name to its OID. A similar result is
   obtained by casting the string to type regnamespace (see Section 8.19);
   however, this function will return NULL rather than throwing an error
   if the name is not found.

   to_regoper ( text ) → regoper

   Translates a textual operator name to its OID. A similar result is
   obtained by casting the string to type regoper (see Section 8.19);
   however, this function will return NULL rather than throwing an error
   if the name is not found or is ambiguous.

   to_regoperator ( text ) → regoperator

   Translates a textual operator name (with parameter types) to its OID. A
   similar result is obtained by casting the string to type regoperator
   (see Section 8.19); however, this function will return NULL rather than
   throwing an error if the name is not found.

   to_regproc ( text ) → regproc

   Translates a textual function or procedure name to its OID. A similar
   result is obtained by casting the string to type regproc (see
   Section 8.19); however, this function will return NULL rather than
   throwing an error if the name is not found or is ambiguous.

   to_regprocedure ( text ) → regprocedure

   Translates a textual function or procedure name (with argument types)
   to its OID. A similar result is obtained by casting the string to type
   regprocedure (see Section 8.19); however, this function will return
   NULL rather than throwing an error if the name is not found.

   to_regrole ( text ) → regrole

   Translates a textual role name to its OID. A similar result is obtained
   by casting the string to type regrole (see Section 8.19); however, this
   function will return NULL rather than throwing an error if the name is
   not found.

   to_regtype ( text ) → regtype

   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 NULL.
   A similar result is obtained by casting the string to type regtype (see
   Section 8.19), except that that will throw error for name not found.

   to_regtypemod ( text ) → integer

   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 NULL.
   The result is -1 if no type modifier is present.

   to_regtypemod can be combined with to_regtype to produce appropriate
   inputs for format_type, allowing a string representing a type name to
   be canonicalized.

   format_type(to_regtype('varchar(32)'), to_regtypemod('varchar(32)')) →
   character varying(32)

   Most of the functions that reconstruct (decompile) database objects
   have an optional pretty flag, which if true causes the result to be
   “pretty-printed”. 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 PostgreSQL; so avoid using
   pretty-printed output for dump purposes. Passing false for the pretty
   parameter yields the same result as omitting the parameter.

   Table 9.77. Index Column Properties
   Name Description
   asc Does the column sort in ascending order on a forward scan?
   desc Does the column sort in descending order on a forward scan?
   nulls_first Does the column sort with nulls first on a forward scan?
   nulls_last Does the column sort with nulls last on a forward scan?
   orderable Does the column possess any defined sort ordering?
   distance_orderable Can the column be scanned in order by a “distance”
   operator, for example ORDER BY col <-> constant ?
   returnable Can the column value be returned by an index-only scan?
   search_array Does the column natively support col = ANY(array)
   searches?
   search_nulls Does the column support IS NULL and IS NOT NULL searches?

   Table 9.78. Index Properties
   Name Description
   clusterable Can the index be used in a CLUSTER command?
   index_scan Does the index support plain (non-bitmap) scans?
   bitmap_scan Does the index support bitmap scans?
   backward_scan Can the scan direction be changed in mid-scan (to support
   FETCH BACKWARD on a cursor without needing materialization)?

   Table 9.79. Index Access Method Properties
   Name Description
   can_order Does the access method support ASC, DESC and related keywords
   in CREATE INDEX?
   can_unique Does the access method support unique indexes?
   can_multi_col Does the access method support indexes with multiple
   columns?
   can_exclude Does the access method support exclusion constraints?
   can_include Does the access method support the INCLUDE clause of CREATE
   INDEX?

   Table 9.80. GUC Flags
   Flag Description
   EXPLAIN Parameters with this flag are included in EXPLAIN (SETTINGS)
   commands.
   NO_SHOW_ALL Parameters with this flag are excluded from SHOW ALL
   commands.
   NO_RESET Parameters with this flag do not support RESET commands.
   NO_RESET_ALL Parameters with this flag are excluded from RESET ALL
   commands.
   NOT_IN_SAMPLE Parameters with this flag are not included in
   postgresql.conf by default.
   RUNTIME_COMPUTED Parameters with this flag are runtime-computed ones.

9.27.5. Object Information and Addressing Functions #

   Table 9.81 lists functions related to database object identification
   and addressing.

   Table 9.81. Object Information and Addressing Functions

   Function

   Description

   pg_get_acl ( classid oid, objid oid, objsubid integer ) → aclitem[]

   Returns the ACL for a database object, specified by catalog OID, object
   OID and sub-object ID. This function returns NULL values for undefined
   objects.

   pg_describe_object ( classid oid, objid oid, objsubid integer ) → text

   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
   pg_depend catalog. This function returns NULL values for undefined
   objects.

   pg_identify_object ( classid oid, objid oid, objsubid integer ) →
   record ( type text, schema text, name text, identity text )

   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. type identifies the type of database object; schema is the
   schema name that the object belongs in, or NULL for object types that
   do not belong to schemas; name 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 NULL; identity 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 NULL values.

   pg_identify_object_as_address ( classid oid, objid oid, objsubid
   integer ) → record ( type text, object_names text[], object_args text[]
   )

   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. type identifies the type of database object; object_names and
   object_args are text arrays that together form a reference to the
   object. These three values can be passed to pg_get_object_address to
   obtain the internal address of the object.

   pg_get_object_address ( type text, object_names text[], object_args
   text[] ) → record ( classid oid, objid oid, objsubid integer )

   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 pg_depend; they can be passed to other system
   functions such as pg_describe_object or pg_identify_object. classid is
   the OID of the system catalog containing the object; objid is the OID
   of the object itself, and objsubid is the sub-object ID, or zero if
   none. This function is the inverse of pg_identify_object_as_address.
   Undefined objects are identified with NULL values.

   pg_get_acl 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:
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}

9.27.6. Comment Information Functions #

   The functions shown in Table 9.82 extract comments previously stored
   with the COMMENT command. A null value is returned if no comment could
   be found for the specified parameters.

   Table 9.82. Comment Information Functions

   Function

   Description

   col_description ( table oid, column integer ) → text

   Returns the comment for a table column, which is specified by the OID
   of its table and its column number. (obj_description cannot be used for
   table columns, since columns do not have OIDs of their own.)

   obj_description ( object oid, catalog name ) → text

   Returns the comment for a database object specified by its OID and the
   name of the containing system catalog. For example,
   obj_description(123456, 'pg_class') would retrieve the comment for the
   table with OID 123456.

   obj_description ( object oid ) → text

   Returns the comment for a database object specified by its OID alone.
   This is deprecated since there is no guarantee that OIDs are unique
   across different system catalogs; therefore, the wrong comment might be
   returned.

   shobj_description ( object oid, catalog name ) → text

   Returns the comment for a shared database object specified by its OID
   and the name of the containing system catalog. This is just like
   obj_description 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.

9.27.7. Data Validity Checking Functions #

   The functions shown in Table 9.83 can be helpful for checking validity
   of proposed input data.

   Table 9.83. Data Validity Checking Functions

   Function

   Description

   Example(s)

   pg_input_is_valid ( string text, type text ) → boolean

   Tests whether the given string is valid input for the specified data
   type, returning true or false.

   This function will only work as desired if the data type's input
   function has been updated to report invalid input as a “soft” error.
   Otherwise, invalid input will abort the transaction, just as if the
   string had been cast to the type directly.

   pg_input_is_valid('42', 'integer') → t

   pg_input_is_valid('42000000000', 'integer') → f

   pg_input_is_valid('1234.567', 'numeric(7,4)') → f

   pg_input_error_info ( string text, type text ) → record ( message text,
   detail text, hint text, sql_error_code text )

   Tests whether the given string 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 pg_input_is_valid.

   This function will only work as desired if the data type's input
   function has been updated to report invalid input as a “soft” error.
   Otherwise, invalid input will abort the transaction, just as if the
   string had been cast to the type directly.

   SELECT * FROM pg_input_error_info('42000000000', 'integer') →
                       message                        | detail | hint | sql_erro
r_code
------------------------------------------------------+--------+------+---------
-------
 value "42000000000" is out of range for type integer |        |      | 22003

9.27.8. Transaction ID and Snapshot Information Functions #

   The functions shown in Table 9.84 provide server transaction
   information in an exportable form. The main use of these functions is
   to determine which transactions were committed between two snapshots.

   Table 9.84. Transaction ID and Snapshot Information Functions

   Function

   Description

   age ( xid ) → integer

   Returns the number of transactions between the supplied transaction id
   and the current transaction counter.

   mxid_age ( xid ) → integer

   Returns the number of multixacts IDs between the supplied multixact ID
   and the current multixacts counter.

   pg_current_xact_id () → xid8

   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 Section 67.1 for details. If
   executed in a subtransaction, this will return the top-level
   transaction ID; see Section 67.3 for details.

   pg_current_xact_id_if_assigned () → xid8

   Returns the current transaction's ID, or NULL 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.

   pg_xact_status ( xid8 ) → text

   Reports the commit status of a recent transaction. The result is one of
   in progress, committed, or aborted, 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 NULL. 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 COMMIT is in progress. Note that prepared transactions are
   reported as in progress; applications must check pg_prepared_xacts if
   they need to determine whether a transaction ID belongs to a prepared
   transaction.

   pg_current_snapshot () → pg_snapshot

   Returns a current snapshot, 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 Section 67.3 for
   details.

   pg_snapshot_xip ( pg_snapshot ) → setof xid8

   Returns the set of in-progress transaction IDs contained in a snapshot.

   pg_snapshot_xmax ( pg_snapshot ) → xid8

   Returns the xmax of a snapshot.

   pg_snapshot_xmin ( pg_snapshot ) → xid8

   Returns the xmin of a snapshot.

   pg_visible_in_snapshot ( xid8, pg_snapshot ) → boolean

   Is the given transaction ID visible 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 Section 67.3 for details.

   pg_get_multixact_members ( multixid xid ) → setof record ( xid xid,
   mode text )

   Returns the transaction ID and lock mode for each member of the
   specified multixact ID. The lock modes forupd, fornokeyupd, sh, and
   keysh correspond to the row-level locks FOR UPDATE, FOR NO KEY UPDATE,
   FOR SHARE, and FOR KEY SHARE, respectively, as described in
   Section 13.3.2. Two additional modes are specific to multixacts:
   nokeyupd, used by updates that do not modify key columns, and upd, used
   by updates or deletes that modify key columns.

   The internal transaction ID type xid is 32 bits wide and wraps around
   every 4 billion transactions. However, the functions shown in
   Table 9.84, except age, mxid_age, and pg_get_multixact_members, use a
   64-bit type xid8 that does not wrap around during the life of an
   installation and can be converted to xid by casting if required; see
   Section 67.1 for details. The data type pg_snapshot stores information
   about transaction ID visibility at a particular moment in time. Its
   components are described in Table 9.85. pg_snapshot's textual
   representation is xmin:xmax:xip_list. For example 10:20:10,14,15 means
   xmin=10, xmax=20, xip_list=10, 14, 15.

   Table 9.85. Snapshot Components
   Name Description
   xmin Lowest transaction ID that was still active. All transaction IDs
   less than xmin are either committed and visible, or rolled back and
   dead.
   xmax One past the highest completed transaction ID. All transaction IDs
   greater than or equal to xmax had not yet completed as of the time of
   the snapshot, and thus are invisible.
   xip_list Transactions in progress at the time of the snapshot. A
   transaction ID that is xmin <= X < xmax 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).

   In releases of PostgreSQL before 13 there was no xid8 type, so variants
   of these functions were provided that used bigint to represent a 64-bit
   XID, with a correspondingly distinct snapshot data type txid_snapshot.
   These older functions have txid in their names. They are still
   supported for backward compatibility, but may be removed from a future
   release. See Table 9.86.

   Table 9.86. Deprecated Transaction ID and Snapshot Information
   Functions

   Function

   Description

   txid_current () → bigint

   See pg_current_xact_id().

   txid_current_if_assigned () → bigint

   See pg_current_xact_id_if_assigned().

   txid_current_snapshot () → txid_snapshot

   See pg_current_snapshot().

   txid_snapshot_xip ( txid_snapshot ) → setof bigint

   See pg_snapshot_xip().

   txid_snapshot_xmax ( txid_snapshot ) → bigint

   See pg_snapshot_xmax().

   txid_snapshot_xmin ( txid_snapshot ) → bigint

   See pg_snapshot_xmin().

   txid_visible_in_snapshot ( bigint, txid_snapshot ) → boolean

   See pg_visible_in_snapshot().

   txid_status ( bigint ) → text

   See pg_xact_status().

9.27.9. Committed Transaction Information Functions #

   The functions shown in Table 9.87 provide information about when past
   transactions were committed. They only provide useful data when the
   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.

   Table 9.87. Committed Transaction Information Functions

   Function

   Description

   pg_xact_commit_timestamp ( xid ) → timestamp with time zone

   Returns the commit timestamp of a transaction.

   pg_xact_commit_timestamp_origin ( xid ) → record ( timestamp timestamp
   with time zone, roident oid)

   Returns the commit timestamp and replication origin of a transaction.

   pg_last_committed_xact () → record ( xid xid, timestamp timestamp with
   time zone, roident oid )

   Returns the transaction ID, commit timestamp and replication origin of
   the latest committed transaction.

9.27.10. Control Data Functions #

   The functions shown in Table 9.88 print information initialized during
   initdb, 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
   pg_controldata application.

   Table 9.88. Control Data Functions

   Function

   Description

   pg_control_checkpoint () → record

   Returns information about current checkpoint state, as shown in
   Table 9.89.

   pg_control_system () → record

   Returns information about current control file state, as shown in
   Table 9.90.

   pg_control_init () → record

   Returns information about cluster initialization state, as shown in
   Table 9.91.

   pg_control_recovery () → record

   Returns information about recovery state, as shown in Table 9.92.

   Table 9.89. pg_control_checkpoint Output Columns
       Column Name             Data Type
   checkpoint_lsn       pg_lsn
   redo_lsn             pg_lsn
   redo_wal_file        text
   timeline_id          integer
   prev_timeline_id     integer
   full_page_writes     boolean
   next_xid             text
   next_oid             oid
   next_multixact_id    xid
   next_multi_offset    xid
   oldest_xid           xid
   oldest_xid_dbid      oid
   oldest_active_xid    xid
   oldest_multi_xid     xid
   oldest_multi_dbid    oid
   oldest_commit_ts_xid xid
   newest_commit_ts_xid xid
   checkpoint_time      timestamp with time zone

   Table 9.90. pg_control_system Output Columns
         Column Name               Data Type
   pg_control_version       integer
   catalog_version_no       integer
   system_identifier        bigint
   pg_control_last_modified timestamp with time zone

   Table 9.91. pg_control_init Output Columns
          Column Name         Data Type
   max_data_alignment         integer
   database_block_size        integer
   blocks_per_segment         integer
   wal_block_size             integer
   bytes_per_wal_segment      integer
   max_identifier_length      integer
   max_index_columns          integer
   max_toast_chunk_size       integer
   large_object_chunk_size    integer
   float8_pass_by_value       boolean
   data_page_checksum_version integer
   default_char_signedness    boolean

   Table 9.92. pg_control_recovery Output Columns
            Column Name          Data Type
   min_recovery_end_lsn          pg_lsn
   min_recovery_end_timeline     integer
   backup_start_lsn              pg_lsn
   backup_end_lsn                pg_lsn
   end_of_backup_record_required boolean

9.27.11. Version Information Functions #

   The functions shown in Table 9.93 print version information.

   Table 9.93. Version Information Functions

   Function

   Description

   version () → text

   Returns a string describing the PostgreSQL server's version. You can
   also get this information from server_version, or for a
   machine-readable version use server_version_num. Software developers
   should use server_version_num (available since 8.2) or PQserverVersion
   instead of parsing the text version.

   unicode_version () → text

   Returns a string representing the version of Unicode used by
   PostgreSQL.

   icu_unicode_version () → text

   Returns a string representing the version of Unicode used by ICU, if
   the server was built with ICU support; otherwise returns NULL

9.27.12. WAL Summarization Information Functions #

   The functions shown in Table 9.94 print information about the status of
   WAL summarization. See summarize_wal.

   Table 9.94. WAL Summarization Information Functions

   Function

   Description

   pg_available_wal_summaries () → setof record ( tli bigint, start_lsn
   pg_lsn, end_lsn pg_lsn )

   Returns information about the WAL summary files present in the data
   directory, under pg_wal/summaries. 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.

   pg_wal_summary_contents ( tli bigint, start_lsn pg_lsn, end_lsn pg_lsn
   ) → setof record ( relfilenode oid, reltablespace oid, reldatabase oid,
   relforknumber smallint, relblocknumber bigint, is_limit_block boolean )

   Returns one information about the contents of a single WAL summary file
   identified by TLI and starting and ending LSNs. Each row with
   is_limit_block 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
   is_limit_block true indicates either that (a) the relation fork was
   truncated to the length given by relblocknumber 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,
   relblocknumber will be zero.

   pg_get_wal_summarizer_state () → record ( summarized_tli bigint,
   summarized_lsn pg_lsn, pending_lsn pg_lsn, summarizer_pid int )

   Returns information about the progress of the WAL summarizer. If the
   WAL summarizer has never run since the instance was started, then
   summarized_tli and summarized_lsn will be 0 and 0/0 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,
   pending_lsn will be the ending LSN of the last record that it has
   consumed, which must always be greater than or equal to summarized_lsn;
   if the WAL summarizer is not running, it will be equal to
   summarized_lsn. summarizer_pid is the PID of the WAL summarizer
   process, if it is running, and otherwise NULL.

   As a special exception, the WAL summarizer will refuse to generate WAL
   summary files if run on WAL generated under wal_level=minimal, 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 wal_level was set to
   replica or higher, it will resume writing summaries to disk.