System Information Functions and Operators

Table 8.54 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 11.1.1 for more information.

Table Session Information Functions

Function Description

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_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 "guc-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_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).
`user` → `name` This is equivalent to `current_user`.
`version` () → `text` Returns a string describing the Tacnode server's version. You can also get this information from "guc-server-version", or for a machine-readable version use "guc-server-version-num". Software developers should use `server_version_num` (available since 8.2) or "libpq-PQserverVersion" instead of parsing the text version.

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_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 "guc-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_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).

user → name

This is equivalent to current_user.

version () → text

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

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 "sql-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 Tacnode does not, since it unifies users and roles into a single kind of entity.)

Table 8.55 lists functions that allow querying object access privileges programmatically. 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 Access Privilege Inquiry Functions

Function Description

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 7.12). 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_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`, and `TRIGGER`.
`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 7.12).

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 7.12). 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_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, and TRIGGER.

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 7.12).

Table 8.56 shows the operators available for the aclitem type, which is the catalog representation of access privileges.

Table aclitem Operators

Operator Description Example(s)

Operator Description Example(s)
`aclitem` `=` `aclitem` → `boolean` Are `aclitem`s 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=rw/hobbes'::aclitem = 'calvin=rw*/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=rw/hobbes,hobbes=rw/postgres}'::aclitem[] @> 'calvin=r/hobbes'::aclitem` → `t`
`aclitem[]` `~` `aclitem` → `boolean` This is a deprecated alias for `@>`. `'}calvin=rw/hobbes,hobbes=rw/postgres}'::aclitem[] ~ 'calvin=r/hobbes'::aclitem` → `t`

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 8.57 shows some additional functions to manage the aclitem type.

Table aclitem Functions

Function Description

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 `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`, '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. Note that each privilege is broken out as a separate row, so only one keyword appears in the `privilege_type` column.

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 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, '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. Note that each privilege is broken out as a separate row, so only one keyword appears in the privilege_type column.

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 Tacnode; so avoid using pretty-printed output for dump purposes. Passing false for the pretty parameter yields the same result as omitting the parameter.

Table 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 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 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`?

The functions shown in Table 8.61 extract comments previously stored with the COMMENT command. A null value is returned if no comment could be found for the specified parameters.

Table Comment Information Functions

Function Description

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
`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.

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

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.

The data type pg_snapshot stores information about transaction ID visibility at a particular moment in time. Its components are described in Table 8.62. 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 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.

Table 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 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 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`

Table 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`

System Information Functions and Operators

System Information Functions and Operators

On this page