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  6. System Information Functions

System Information Functions

Session Information Functions

  • current_catalog

    Description: Name of the current database (called "catalog" in the SQL standard)

    Return type: name

    For example:

    SELECT current_catalog;
     current_database
    ------------------
     postgres
    (1 row)
  • current_database()

    Description: Name of the current database

    Return type: name

    For example:

    SELECT current_database();
     current_database
    ------------------
     postgres
    (1 row)
  • current_query()

    Description: Text of the currently executing query, as submitted by the client (might contain more than one statement)

    Return type: text

    For example:

    SELECT current_query();
          current_query
    -------------------------
     SELECT current_query();
    (1 row)
  • current_schema()

    Description: Name of current schema

    Return type: name

    For example:

    SELECT current_schema();
     current_schema
    ----------------
     public
    (1 row)

    Remarks: the current_schema function returns the first valid schema in the search path. If the search path is empty or contains no valid schema name, NULL is returned.) 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(boolean)

    Description: Names of schemas in search path

    Return type: name[]

    For example:

    SELECT current_schemas(true);
       current_schemas
    ---------------------
     {pg_catalog,public}
    (1 row)

    Note:

    current_schemas(boolean) returns an array of the names of all schemas presently in the search path. The Boolean option determines whether implicitly included system schemas such as pg_catalog are included in the returned search path.

    NOTE:

    The search path can be altered at run time by running the following command:

    SET search_path TO schema [, schema, ...]
  • current_user

    Description: User name of current execution context

    Return type: name

    For example:

    SELECT current_user;
     current_user
    --------------
     dbadmin
    (1 row)

    Note: 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.

  • inet_client_addr()

    Description: Remote connection address. inet_client_addr returns the IP address of the current client.

    NOTE:

    It is available only in remote connection mode.

    Return type: inet

    For example:

    SELECT inet_client_addr();
     inet_client_addr
    ------------------
     10.10.0.50
    (1 row)
  • inet_client_port()

    Description:

    Port of the remote connection And inet_client_port returns the port number.

    NOTE:

    It is available only in remote connection mode.

    Return type: int

    For example:

    SELECT inet_client_port();
     inet_client_port
    ------------------
                33143
    (1 row)
  • inet_server_addr()

    Description:

    Address of the local connection inet_server_addr returns the IP address on which the server accepted the current connection.

    NOTE:

    It is available only in remote connection mode.

    Return type: inet

    For example:

    SELECT inet_server_addr();
     inet_server_addr
    ------------------
     10.10.0.13
    (1 row)
  • inet_server_port()

    Description:

    Port of the local connection inet_server_port returns the port number. All these functions return NULL if the current connection is via a Unix-domain socket.

    NOTE:

    It is available only in remote connection mode.

    Return type: int

    For example:

    SELECT inet_server_port();
     inet_server_port
    ------------------
     8000
    (1 row)
  • pg_backend_pid()

    Description: Process ID of the server process attached to the current session

    Return type: int

    For example:

    SELECT pg_backend_pid();
     pg_backend_pid
    -----------------
     140229352617744
    (1 row)
  • pg_conf_load_time()

    Description: Configures load time. pg_conf_load_time returns the timestamp with time zone when the server configuration files were last loaded.

    Return type: timestamp with time zone

    For example:

    SELECT pg_conf_load_time();
          pg_conf_load_time       
    ------------------------------
     2017-09-01 16:05:23.89868+08
    (1 row)
  • pg_my_temp_schema()

    Description: OID of the temporary schema of a session. The value is 0 if the OID does not exist.

    Return type: OID

    For example:

    SELECT pg_my_temp_schema();
     pg_my_temp_schema 
    -------------------
                     0
    (1 row)

    Note: pg_my_temp_schema 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 returns true if the given OID is the OID of another session's temporary schema.

  • pg_is_other_temp_schema(oid)

    Description: Whether the schema is the temporary schema of another session.

    Return type: Boolean

    For example:

    SELECT pg_is_other_temp_schema(25356);
     pg_is_other_temp_schema
    -------------------------
     f
    (1 row)
  • pg_listening_channels()

    Description: Channel names that the session is currently listening on

    Return type: setof text

    For example:

    SELECT pg_listening_channels();
     pg_listening_channels
    -----------------------
    (0 rows)

    Note: pg_listening_channels returns a set of names of channels that the current session is listening to.

  • pg_postmaster_start_time()

    Description: Server start time pg_postmaster_start_time returns the timestamp with time zone when the server started.

    Return type: timestamp with time zone

    For example:

    SELECT pg_postmaster_start_time();
       pg_postmaster_start_time   
    ------------------------------
     2017-08-30 16:02:54.99854+08
    (1 row)
  • pg_trigger_depth()

    Description: Current nesting level of triggers

    Return type: int

    For example:

    SELECT pg_trigger_depth();
     pg_trigger_depth 
    ------------------
                    0
    (1 row)
  • pgxc_version()

    Description: Postgres-XC version information

    Return type: text

    For example:

    SELECT pgxc_version();
                                                    pgxc_version                                                 
    -------------------------------------------------------------------------------------------------------------
     Postgres-XC 1.1 on x86_64-unknown-linux-gnu, based on PostgreSQL 9.2.4, compiled by g++ (GCC) 5.4.0, 64-bit
    (1 row)
  • session_user

    Description: Session user name

    Return type: name

    For example:

    SELECT session_user;
     session_user
    --------------
     dbadmin
    (1 row)

    Note: session_user is usually the user who initiated the current database connection, but administrators can change this setting with SET SESSION AUTHORIZATION.

  • user

    Description: Equivalent to current_user.

    Return type: name

    For example:

    SELECT user;
     current_user
    --------------
     dbadmin
    (1 row)
  • version()

    Description: Version information. version returns a string describing a server's version.

    Return type: text

    For example:

    SELECT version();
                                                                    version                                                                
    ---------------------------------------------------------------------------------------------------------------------------------------
     Gauss200 V100R007C10 build 7268 compiled at 2018-01-29 10:44:43 on x86_64-unknown-linux-gnu, compiled by g++ (GCC) 5.4.0, 64-bit
    (1 row)

Access Privilege Inquiry Functions

  • has_any_column_privilege(user, table, privilege)

    Description: Queries whether a specified user has permission for any column of table.

    Return type: Boolean

  • has_any_column_privilege(table, privilege)

    Description: Queries whether the current user has permission for any column of table.

    Return type: Boolean

    has_any_column_privilege checks whether a user can access any column of a table in a particular way. Its parameter possibilities are analogous to has_table_privilege, except that the desired access permission type must be some combination of SELECT, INSERT, UPDATE, or REFERENCES.

    NOTE:

    Note that having any of these permissions at the table level implicitly grants it for each column of the table, so has_any_column_privilege will always return true if has_table_privilege does for the same parameters. But has_any_column_privilege also succeeds if there is a column-level grant of the permission for at least one column.

  • has_column_privilege(user, table, column, privilege)

    Description: Queries whether a specified user has permission for column.

    Return type: Boolean

  • has_column_privilege(table, column, privilege)

    Description: Queries whether the current user has permission for column.

    Return type: Boolean

    has_column_privilege checks whether a user can access a column in a particular way. Its argument possibilities are analogous to has_table_privilege, with the addition that the column can be specified either by name or attribute number. The desired access permission type must evaluate to some combination of SELECT, INSERT, UPDATE, or REFERENCES.

    NOTE:

    Note that having any of these permissions at the table level implicitly grants it for each column of the table.

  • has_database_privilege(user, database, privilege)

    Description: Queries whether a specified user has permission for database.

    Return type: Boolean

  • has_database_privilege(database, privilege)

    Description: Queries whether the current user has permission for database.

    Return type: Boolean

    Note: has_database_privilege checks whether a user can access a database in a particular way. Its argument possibilities are analogous to has_table_privilege. The desired access permission type must evaluate to some combination of CREATE, CONNECT, TEMPORARY, or TEMP (which is equivalent to TEMPORARY).

  • has_foreign_data_wrapper_privilege(user, fdw, privilege)

    Description: Queries whether a specified user has permission for foreign-data wrapper.

    Return type: Boolean

  • has_foreign_data_wrapper_privilege(fdw, privilege)

    Description: Queries whether the current user has permission for foreign-data wrapper.

    Return type: Boolean

    Note: has_foreign_data_wrapper_privilege checks whether a user can access a foreign-data wrapper in a particular way. Its argument possibilities are analogous to has_table_privilege. The desired access permission type must evaluate to USAGE.

  • has_function_privilege(user, function, privilege)

    Description: Queries whether a specified user has permission for function.

    Return type: Boolean

  • has_function_privilege(function, privilege)

    Description: Queries whether the current user has permission for function.

    Return type: Boolean

    Note: has_function_privilege checks whether a user can access a function in a particular way. Its argument possibilities are analogous to has_table_privilege. When a function is specified by a text string rather than by OID, the allowed input is the same as that for the regprocedure data type (see Object Identifier Types). The desired access permission type must evaluate to EXECUTE.

  • has_language_privilege(user, language, privilege)

    Description: Queries whether a specified user has permission for language.

    Return type: Boolean

  • has_language_privilege(language, privilege)

    Description: Queries whether the current user has permission for language.

    Return type: Boolean

    Note: has_language_privilege checks whether a user can access a procedural language in a particular way. Its argument possibilities are analogous to has_table_privilege. The desired access permission type must evaluate to USAGE.

  • has_schema_privilege(user, schema, privilege)

    Description: Queries whether a specified user has permission for schema.

    Return type: Boolean

  • has_schema_privilege(schema, privilege)

    Description: Queries whether the current user has permission for schema.

    Return type: Boolean

    Note: has_schema_privilege checks whether a user can access a schema in a particular way. Its argument possibilities are analogous to has_table_privilege. The desired access permission type must evaluate to some combination of CREATE or USAGE.

  • has_server_privilege(user, server, privilege)

    Description: Queries whether a specified user has permission for foreign server.

    Return type: Boolean

  • has_server_privilege(server, privilege)

    Description: Queries whether the current user has permission for foreign server.

    Return type: Boolean

    Note: has_server_privilege checks whether a user can access a foreign server in a particular way. Its argument possibilities are analogous to has_table_privilege. The desired access permission type must evaluate to USAGE.

  • has_table_privilege(user, table, privilege)

    Description: Queries whether a specified user has permission for table.

    Return type: Boolean

  • has_table_privilege(table, privilege)

    Description: Queries whether the current user has permission for table.

    Return type: Boolean

    has_table_privilege checks whether a user can access a table in a particular way. The user can be specified by name, by OID (pg_authid.oid), public to indicate the PUBLIC pseudo-role, or if the argument is omitted current_user is assumed. The table can be specified by name or by OID. When specifying by name, the name can be schema-qualified if necessary. The desired access permission type is specified by a text string, which must be one of the values SELECT, INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, or TRIGGER. Multiple privilege types can be listed with separated by commas, in which case the result will be true if any of the listed privileges is held.

    For example:

    SELECT has_table_privilege('tpcds.web_site', 'select');
     has_table_privilege  
    --------------------- 
     t 
    (1 row)
    
    SELECT has_table_privilege('dbadmin', 'tpcds.web_site', 'select,insert ');
     has_table_privilege  
    --------------------- 
     t 
    (1 row) 
    
  • pg_has_role(user, role, privilege)

    Description: Queries whether a specified user has permission for role.

    Return type: Boolean

  • pg_has_role(role, privilege)

    Description: Specifies whether the current user has permission for role.

    Return type: Boolean

    Note: pg_has_role checks whether a user can access a role in a particular way. Its argument possibilities are analogous to has_table_privilege, except that public is not allowed as a user name. The desired access permission type must evaluate to some combination of MEMBER or USAGE. MEMBER denotes direct or indirect membership in the role (that is, the right to do SET ROLE), while USAGE denotes the permissions of the role are available without doing SET ROLE.

Schema Visibility Inquiry Functions

Each function performs the visibility check for one type of database object. For functions and operators, an object in the search path is visible if there is no object of the same name and argument data type(s) earlier in the path. For operator classes, both name and associated index access method are considered.

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, 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. For example, to list the names of all visible tables:

SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
  • pg_collation_is_visible(collation_oid)

    Description: Queries whether the collation is visible in search path.

    Return type: Boolean

  • pg_conversion_is_visible(conversion_oid)

    Description: Queries whether the conversion is visible in search path.

    Return type: Boolean

  • pg_function_is_visible(function_oid)

    Description: Queries whether the function is visible in search path.

    Return type: Boolean

  • pg_opclass_is_visible(opclass_oid)

    Description: Queries whether the operator class is visible in search path.

    Return type: Boolean

  • pg_operator_is_visible(operator_oid)

    Description: Queries whether the operator is visible in search path.

    Return type: Boolean

  • pg_opfamily_is_visible(opclass_oid)

    Description: Queries whether the operator family is visible in search path.

    Return type: Boolean

  • pg_table_is_visible(table_oid)

    Description: Queries whether the table is visible in search path.

    Return type: Boolean

  • pg_ts_config_is_visible(config_oid)

    Description: Queries whether the text search configuration is visible in search path.

    Return type: Boolean

  • pg_ts_dict_is_visible(dict_oid)

    Description: Queries whether the text search dictionary is visible in search path.

    Return type: Boolean

  • pg_ts_parser_is_visible(parser_oid)

    Description: Queries whether the text search parser is visible in search path.

    Return type: Boolean

  • pg_ts_template_is_visible(template_oid)

    Description: Queries whether the text search template is visible in search path.

    Return type: Boolean

  • pg_type_is_visible(type_oid)

    Description: Queries whether the type (or domain) is visible in search path.

    Return type: Boolean

System Catalog Information Functions

  • format_type(type_oid, typemod)

    Description: Gets SQL name of a data type.

    Return type: text

    Note:

    format_type returns the SQL name of 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. Certain type modifiers are passed for data types with length limitations. The SQL name returned from format_type contains the length of the data type, which can be calculated by taking sizeof(int32) from actual storage length [actual storage len - sizeof(int32)] in the unit of bytes. 32-bit space is required to store the customized length set by users. So the actual storage length contains 4 bytes more than the customized length. In the following example, the SQL name returned from format_type is character varying(6), indicating the length of varchar type is 6 bytes. So the actual storage length of varchar type is 10 bytes.

    SELECT format_type((SELECT oid FROM pg_type WHERE typname='varchar'), 10);
         format_type      
    ----------------------
     character varying(6)
    (1 row)
  • pg_describe_object(catalog_id, object_id, object_sub_id)

    Description: Gets description of a database object.

    Return type: text

    Note: pg_describe_object returns a description of a database object specified by catalog OID, object OID and a (possibly zero) sub-object ID. This is useful to determine the identity of an object as stored in the pg_depend catalog.

  • pg_get_constraintdef(constraint_oid)

    Description: Gets definition of a constraint.

    Return type: text

  • pg_get_constraintdef(constraint_oid, pretty_bool)

    Description: Gets definition of a constraint.

    Return type: text

    Note: pg_get_constraintdef and pg_get_indexdef respectively reconstruct the creating command for a constraint and an index.

  • pg_get_expr(pg_node_tree, relation_oid)

    Description: Decompiles internal form of an expression, assuming that any Vars in it refer to the relationship indicated by the second parameter.

    Return type: text

  • pg_get_expr(pg_node_tree, relation_oid, pretty_bool)

    Description: Decompiles internal form of an expression, assuming that any Vars in it refer to the relationship indicated by the second parameter.

    Return type: text

    Note: pg_get_expr decompiles the internal form of an individual expression, such as the default value for a column. It can be useful when examining the contents of system catalogs. If the expression might contain Vars, specify the OID of the relationship they refer to as the second parameter; if no Vars are expected, zero is sufficient.

  • pg_get_functiondef(func_oid)

    Description: Gets definition of a function.

    Return type: text

  • pg_get_function_arguments(func_oid)

    Description: Gets argument list of function's definition (with default values).

    Return type: text

    Note: pg_get_function_arguments returns the argument list of a function, in the form it would need to appear in within CREATE FUNCTION.

  • pg_get_function_identity_arguments(func_oid)

    Description: Gets argument list to identify a function (without default values).

    Return type: text

    Note: pg_get_function_identity_arguments returns the argument list necessary to identify a function, in the form it would need to appear in within ALTER FUNCTION. This form omits default values.

  • pg_get_function_result(func_oid)

    Description: Gets RETURNS clause for function.

    Return type: text

    Note: pg_get_function_result returns the appropriate RETURNS clause for the function.

  • pg_get_indexdef(index_oid)

    Description: Gets CREATE INDEX command for index.

    Return type: text

  • pg_get_indexdef(index_oid, column_no, pretty_bool)

    Description: Gets CREATE INDEX command for index, or definition of just one index column when column_no is not zero.

    Return type: text

    Note: pg_get_functiondef returns a complete CREATE OR REPLACE FUNCTION statement for a function.

  • pg_get_keywords()

    Description: Gets list of SQL keywords and their categories.

    Return type: setof record

    Note: pg_get_keywords 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 unreserved, C for column name, T for type or function name, or R for reserved. The catdesc column contains a possibly-localized string describing the category.

  • pg_get_ruledef(rule_oid)

    Description: Gets CREATE RULE command for a rule.

    Return type: text

  • pg_get_ruledef(rule_oid, pretty_bool)

    Description: Gets CREATE RULE command for a rule.

    Return type: text

  • pg_get_userbyid(role_oid)

    Description: Gets role name with given OID.

    Return type: name

    Note: pg_get_userbyid extracts a role's name given its OID.

  • pg_get_viewdef(view_name)

    Description: Gets underlying SELECT command for view.

    Return type: text

  • pg_get_viewdef(view_name, pretty_bool)

    Description: Gets underlying SELECT command for view, lines with columns are wrapped to 80 columns if pretty_bool is true.

    Return type: text

    Note: pg_get_viewdef reconstructs the SELECT query that defines a view. Most of these functions come in two variants. When the function has the parameter pretty_bool and the value is true, it can optionally "pretty-print" the result. The pretty-printed format is more readable. The other one is default format which is more likely to be interpreted the same way by future versions of PostgreSQL. Avoid using pretty-printed output for dump purposes. Passing false for the pretty-print parameter yields the same result as the variant that does not have the parameter at all.

  • pg_get_viewdef(view_oid)

    Description: Gets underlying SELECT command for view.

    Return type: text

  • pg_get_viewdef(view_oid, pretty_bool)

    Description: Gets underlying SELECT command for view, lines with columns are wrapped to 80 columns if pretty_bool is true.

    Return type: text

  • pg_get_viewdef(view_oid, wrap_column_int)

    Description: Gets underlying SELECT command for view, wrapping lines with columns as specified, printing is implied.

    Return type: text

  • pg_options_to_table(reloptions)

    Description: Gets the set of storage option name/value pairs.

    Return type: setof record

    Note: pg_options_to_table returns the set of storage option name/value pairs (option_name/option_value) when passed pg_class.reloptions or pg_attribute.attoptions.

  • pg_typeof(any)

    Description: Gets the data type of any value.

    Return type: regtype

    Note:

    pg_typeof 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 Object Identifier Types). This means that it is the same as an OID for comparison purposes but displays as a type name.

    For example:

    SELECT pg_typeof(33);
     pg_typeof 
    -----------
     integer
    (1 row)
    
    SELECT typlen FROM pg_type WHERE oid = pg_typeof(33);
     typlen 
    --------
          4
    (1 row)
  • collation for (any)

    Description: Gets the collation of the parameter.

    Return type: text

    Note:

    The expression collation for returns the collation of the value that is passed to it. For example:

    SELECT collation for (description) FROM pg_description LIMIT 1;
     pg_collation_for 
    ------------------
     "default"
    (1 row)

    The value might be quoted and schema-qualified. If no collation is derived for the argument expression, then a null value is returned. If the parameter is not of a collatable data type, then an error is thrown.

  • getdistributekey(table_name)

    Description: Gets a distribution column for a hash table.

    Return type: text

    For example:

    SELECT getdistributekey('item');
     getdistributekey 
    ------------------
     i_item_sk
    (1 row)

Comment Information Functions

  • col_description(table_oid, column_number)

    Description: Gets comment for a table column.

    Return type: text

    Note: col_description returns the comment for a table column, which is specified by the OID of its table and its column number.

  • obj_description(object_oid, catalog_name)

    Description: Gets comment for a shared database object.

    Return type: text

    Note: The two-parameter form of obj_description 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. The one-parameter form of obj_description requires only the object OID.

    obj_description cannot be used for table columns since columns do not have OIDs of their own.

  • obj_description(object_oid)

    Description: Gets comment for a shared database object.

    Return type: text

  • shobj_description(object_oid, catalog_name)

    Description: Gets comment for a shared database object.

    Return type: text

    Note: shobj_description is used just like obj_description except the former is used for retrieving comments on shared objects. Some system catalogs are global to all databases within each cluster, and the comments for objects in them are stored globally as well.

Transaction IDs and Snapshots

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

  • pgxc_is_committed(transaction_id)

    Description: When the given XID (gxid) is committed or ignored. NULL indicates the unknown status (such as running, preparing, and freezing).

    Return type: bool

  • txid_current()

    Description: Gets current transaction ID.

    Return type: bigint

  • txid_current_snapshot()

    Description: Gets current snapshot.

    Return type: txid_snapshot

  • txid_snapshot_xip(txid_snapshot)

    Description: Gets in-progress transaction IDs in snapshot.

    Return type: setof bigint

  • txid_snapshot_xmax(txid_snapshot)

    Description: Gets xmax of snapshot.

    Return type: bigint

  • txid_snapshot_xmin(txid_snapshot)

    Description: Gets xmin of snapshot.

    Return type: bigint

  • txid_visible_in_snapshot(bigint, txid_snapshot)

    Description: Queries whether the transaction ID is visible in snapshot. (do not use with subtransaction ids)

    Return type: Boolean

  

The internal transaction ID type (xid) is 32 bits wide and wraps around every 4 billion transactions. The data type used by these functions, txid_snapshot, stores information about transaction ID visibility at a particular moment in time. Table 1 describes its components.

Table 1 Snapshot components

Name

Description

xmin

Earliest transaction ID (txid) that is still active. All earlier transactions will either be committed and visible, or rolled back.

xmax

First as-yet-unassigned txid. All txids greater than or equal to this are not yet started as of the time of the snapshot, so they are invisible.

xip_list

Active txids at the time of the snapshot. The list includes only those active txids between xmin and xmax; there might be active txids higher than xmax. A txid that is xmin <= txid < xmax and not in this list was already completed at the time of the snapshot, and is either visible or dead according to its commit status. The list does not include txids of subtransactions.

txid_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.

Computing Node Group Function

pv_compute_pool_workload()

Description: Load status of a computing Node Group.

Return type: void

Example:

SELECT * from pv_compute_pool_workload();
 nodename  | rpinuse | maxrp | nodestate
-----------+---------+-------+-----------
 datanode1 |       0 |  1000 | normal
 datanode2 |       0 |  1000 | normal
(2 rows)