Help Center/ GaussDB(DWS)/ SQL Syntax Reference (9.1.0.x)/ Functions and Operators/ System Administration Functions/ Other Functions
Updated on 2024-12-18 GMT+08:00
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Other Functions

pgxc_pool_check()

Description: Checks whether the connection data buffered in the pool is consistent with pgxc_node. This parameter has been discarded in 8.3.0 and later cluster versions.

Return type: boolean

pgxc_pool_reload()

Description: Updates the connection information buffered in the pool.

Return type: boolean

pgxc_lock_for_backup()

Description: Locks the cluster before backup. Backup is performed to restore data on new nodes.

Return type: boolean

pgxc_lock_for_backup locks a cluster before gs_dump or gs_dumpall is used to back up the cluster. After a cluster is locked, operations changing the system structure are not allowed. This function does not affect DML statements.

pg_pool_validate(clear boolean, co_node_name cstring)

Description: Clears invalid backend threads on a CN. (These backend threads hold invalid pooler connections to standby DNs.)

Return type: record

pg_nodes_memory()

Description: queries the memory usage of all nodes.

Return type: record

table_skewness(text)

Description: queries the percentage of table data among all nodes.

Parameter: Indicates that the type of the name of the to-be-queried table is text.

Return type: record

table_skewness(table_name text, column_name text[, row_num text])

Description: Queries the proportion of column data distributed on each node based on the hash distribution rule. The results are sorted based on the data volumes of the nodes.

Parameters: table_name indicates a table name, column_name indicates a column name, and row_num indicates that all data in the current column is returned. The default value is 0. A value other than 0 indicates the number of data records whose statistics are sampled. (Records are randomly sampled.)

Return type: record

Example:

Distribute data by hash based on the a column in the tx table. Seven records are distributed on DN 1, two records on DN 2, and one record on DN 0.

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SELECT * FROM table_skewness('tx','a');
 seqnum | num |  ratio
--------+-----+----------
 1      | 7   | 70.000%
 2      | 2   | 20.000%
 0      | 1   | 10.000%
(3 row)

table_data_skewness(data_row record, locatorType "char")

Description: Calculates the bucket distribution index for the records concatenated using the columns in a specified table.

Parameters: data_row indicates the record concatenated using columns in the specified table. locatorType indicates the distribution rule. You are advised to set locatorType to H, indicating hash distribution.

Return type: smallint

Example:

Calculates the bucket distribution index based on the hash distribution rule for the records combined concatenated using column a in the tx table.

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select a, table_data_skewness(row(a), 'H') from tx;
 a | table_data_skewness 
---+---------------------
 3 |                   0
 6 |                   2
 7 |                   2
 4 |                   1
 5 |                   1
(5 rows)

table_distribution(schemaname text, tablename text)

Description: queries the storage space occupied by a specified table on each node.

Parameter: Indicates that the types of the schema name and table name for the table to be queried are both text.

Return type: record

  • To query for the storage distribution of a specified table by using this function, you must have the SELECT permission for the table.
  • The performance of table_distribution is better than that of table_skewness. Especially in a large cluster with a large amount of data, table_distribution is recommended.
  • When you use table_distribution and want to view the space usage, you can use dnsize or (sum(dnsize) over ()) to view the percentage.

table_distribution(regclass)

Description: queries the storage space occupied by a specified table on each node.

Parameter: indicates the name or OID of the table to be queried. The table name can be defined by the schema name. Parameter type: regclass

Return type: record

  • To query for the storage distribution of a specified table by using this function, you must have the SELECT permission for the table.
  • The performance of table_distribution is better than that of table_skewness. Especially in a large cluster with a large amount of data, table_distribution is recommended.
  • When you use table_distribution and want to view the space usage, you can use dnsize or (sum(dnsize) over ()) to view the percentage.

table_distribution()

Description: queries the storage distribution of all tables in the current database.

Return type: record

  • This function involves the query for information about all tables in the database. To execute this function, you must have the administrator rights or rights of the preset role gs_role_read_all_stats.
  • Based on the table_distribution() function, GaussDB(DWS) provides the PGXC_GET_TABLE_SKEWNESS view as an alternative way to query for data skew. You are advised to use this view when the number of tables in the database is less than 10000.

gs_table_distribution(schemaname text, tablename text)

Description: queries the storage space occupied by a specified table on each node.

Return type: record

Table 1 Fields returned by the gs_table_distribution(schemaname text, tablename text) function

Name

Type

Description

schemaname

name

Schema name

tablename

name

Table name

relkind

character

Type.

  • i: index
  • r: table

nodename

name

Node name

dnsize

bigint

Storage space of the table on the node, in bytes.
  • To query for the storage distribution of a specified table by using this function, you must have the SELECT permission for the table.
  • This function is based on the physical file storage space records in the PG_RELFILENODE_SIZE system catalog. Ensure that the GUC parameters use_workload_manager and enable_perm_space are enabled.
  • The gs_table_distribution function performs slower than the table_distribution function when querying a single table. However, when querying the entire database, the gs_table_distribution function shows significantly better performance. For large clusters with a substantial amount of data, it is recommended to use the gs_table_distribution function to query all tables in the database.

gs_table_distribution()

Description: quickly queries the storage distribution of all tables in the current database.

Return type: record

Table 2 Fields returned by the gs_table_distribution() function

Name

Type

Description

schemaname

name

Schema name

tablename

name

Table name

relkind

character

Type of the table. i: index; r: table.

nodename

name

Node name

dnsize

bigint

Storage space of the table on the node, in bytes.
  • To query for the storage distribution of a specified table by using this function, you must have the SELECT permission for the table.
  • This function is based on the physical file storage space records in the PG_RELFILENODE_SIZE system catalog. Ensure that the GUC parameters use_workload_manager and enable_perm_space are enabled.
  • The gs_table_distribution function performs slower than the table_distribution function when querying a single table. However, when querying the entire database, the gs_table_distribution function shows significantly better performance. For large clusters with a substantial amount of data, it is recommended to use the gs_table_distribution function to query all tables in the database.
  • Based on the gs_table_distribution() function, GaussDB(DWS) 8.2.1 and later versions provide the PGXC_WLM_TABLE_DISTRIBUTION_SKEWNESS view for data skew query. You are advised to use this view when the number of tables in the database is small (less than 10,000).

check_foreign_key_constraint(schema.table)

Description: Checks whether data in a foreign key table meets foreign key constraints. This is supported only by clusters of version 9.1.0.200 or later.

Return type: text

Example:

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set info_constraint_options = 'foreign_key';

CREATE TABLE ptt1 (a int,b int,e varchar(50),f varchar(50),PRIMARY KEY (a,b)) DISTRIBUTE BY HASH(a,b);
CREATE TABLE tt2 (a int , b int, c int, d int) DISTRIBUTE BY HASH(a,b);

select check_foreign_key_constraint('table_constraints.tt2');
check_foreign_key_constraint
-----------------------------------------
tt2 table has no foreign key constraint

ALTER TABLE tt2 ADD CONSTRAINT fk_tt1_a FOREIGN KEY (a,b) REFERENCES ptt1(a,b);

select check_foreign_key_constraint('table_constraints.tt2');
check_foreign_key_constraint
-------------------------------------------
tt2 satisfied all Foreign key constraints

plan_seed()

Description: Obtains the seed value of the previous query statement (internal use).

Return type: integer

pg_stat_get_env()

Description: Obtains the environment variable information about the current node.

Return type: record

pg_stat_get_thread()

Description: Provides information about the status of all threads under the current node.

Return type: record

pgxc_get_os_threads()

Description: Provides information about the status of threads under all normal nodes in a cluster.

Return type: record

pg_stat_get_sql_count()

Description: Provides statistics on the number of SELECT/UPDATE/INSERT/DELETE/MERGE INTO statements executed by all users on the current node, response time, and the number of DDL, DML, and DCL statements.

Return type: record

pgxc_get_sql_count()

Description: Provides statistics on the number of SELECT/UPDATE/INSERT/DELETE/MERGE INTO statements executed by all users on all nodes of the current cluster, response time, and the number of DDL, DML, and DCL statements.

Return type: record

pgxc_get_workload_sql_count()

Description: Provides statistics on the number of SELECT/UPDATE/INSERT/DELETE statements executed in all workload Cgroup on all CNs of the current cluster and the number of DDL, DML, and DCL statements.

Return type: record

pgxc_get_workload_sql_elapse_time()

Description: Provides statistics on response time of SELECT/UPDATE/INSERT/DELETE statements executed in all workload Cgroup on all CNs of the current cluster.

Return type: record

get_instr_unique_sql()

Description: Provides information about Unique SQL statistics collected on the current node. If the node is a CN, the system returns the complete information about the Unique SQL statistics collected on the CN. That is, the system collects and summarizes the information about the Unique SQL statistics on other CNs and DNs. If the node is a DN, the Unique SQL statistics on the DN is returned. For details, see the GS_INSTR_UNIQUE_SQL view.

Return type: record

reset_instr_unique_sql(cstring, cstring, INT8)

Description: Clears collected Unique SQL statistics. The input parameters are described as follows:

  • GLOBAL/LOCAL: Data is cleared from all nodes or the current node.
  • ALL/BY_USERID/BY_CNID/BY_GUC: ALL indicates that all data is cleared. BY_USERID/BY_CNID indicates that data is cleared by USERID or CNID. BY_GUC indicates that the clearance operation is caused by the decrease of the value of the GUC parameter instr_unique_sql_count.
  • The third parameter corresponds to the second parameter. The parameter is invalid for ALL/BY_GUC.

Return type: bool

pgxc_get_instr_unique_sql()

Description: Provides complete information about Unique SQL statistics collected on all CNs in a cluster. This function can be executed only on CNs.

Return type: record

get_instr_unique_sql_remote_cns()

Description: Provides complete information about Unique SQL statements collected on all CNs in the cluster, except the CN on which the function is being executed. This function can be executed only on CNs.

Return type: record

pgxc_get_node_env()

Description: Provides the environment variable information about all nodes in a cluster.

Return type: record

gs_switch_relfilenode()

Description: Exchanges meta information of two tables or partitions. (This is only used for the redistribution tool. An error message is displayed when the function is directly used by users).

Return type: integer

copy_error_log_create()

Description: Creates the error table (public.pgxc_copy_error_log) required for creating the COPY FROM error tolerance mechanism.

Return type: boolean

  • This function attempts to create the public.pgxc_copy_error_log table. For details about the table, see Table 3.
  • Create the B-tree index on the relname column and execute REVOKE ALL on public.pgxc_copy_error_log FROM public to manage permissions for the error table (the permissions are the same as those of the COPY statement).
  • public.pgxc_copy_error_log is a row-store table. Therefore, this function can be executed and COPY FROM error tolerance is available only when row-store tables can be created in the cluster. After the GUC parameter enable_hadoop_env is enabled, row-based tables cannot be created in the cluster. The default value is off.
  • Same as the error table and the COPY statement, the function requires sysadmin or higher permissions.
  • If the public.pgxc_copy_error_log table or the copy_error_log_relname_idx index already exists before the function creates it, the function will report an error and roll back.
Table 3 Error table public.pgxc_copy_error_log

Column

Type

Description

relname

varchar

Table name in the form of Schema name.Table name

begintime

timestamp with time zone

Time when a data format error was reported

filename

varchar

Name of the source data file where a data format error occurs

rownum

bigint

Number of the row where a data format error occurs in a source data file

rawrecord

text

Raw record of a data format error in the source data file To prevent a field from being too long, the length of the field cannot exceed 1024 bytes.

detail

text

Error details

columnname

varchar

Name of the column whose data format is incorrect in the data source file. Only 8.2.1.100 and later versions support this function.

errcode

varchar

Error code corresponding to the error information. The sqlstate error code is used. Only 8.2.1.100 and later versions support this function.

queryid

bigint

ID of the SQL statement for executing the Copy statement. It uniquely identifies an SQL statement. Only 8.2.1.100 and later versions support this function.

pv_compute_pool_workload()

Description: Provides the current load information about computing Node Groups on cloud.

Return type: record

pg_stat_get_status(tid, num_node_display)

Description: Queries for the blocking and waiting status of the backend threads and auxiliary threads in the current instance. For details about the returned results, see the PG_THREAD_WAIT_STATUS view. The input parameters are described as follows:

  • tid: thread ID, which is of the bigint type. If this parameter is null, the waiting statuses of all backend threads and auxiliary threads are returned. Otherwise, only the waiting statuses of threads with the specified IDs are returned.
  • num_node_display: integer type. Specifies the maximum number of waiting nodes displayed in the wait_status column for records whose waiting status is wait node.
    • If this parameter is left empty or set to a value less than or equal to 0, only one waiting node is displayed.
    • If the value is greater than 20, a maximum number of nodes can be displayed is 20.
    • If the value is greater than 0 and less than or equal to 20, the smaller value between num_node_display and the actual number of waiting nodes is displayed. Use the SELECT * from pg_stat_get_status(NULL, 10) query for example. If the number of waiting nodes is greater than 10, the names of only 10 nodes are displayed randomly. If the number of waiting nodes is less than or equal to 10, the names of all waiting nodes are displayed. If the number of waiting nodes is greater than the number of displayed nodes, the displayed node names are randomly selected.

Return type: record

pgxc_get_thread_wait_status(num_node_display)

Description: Queries for the call hierarchy between threads generated by all SQL statements on each node in a cluster, as well as the block waiting status of each thread. For details about the returned results, see the PGXC_THREAD_WAIT_STATUS view. The type and meaning of the input parameter num_node_display are the same as those of the pg_stat_get_status function.

Return type: record

pgxc_os_run_info()

Description: Obtains the running status of the operating system on each node in a cluster. For details about the returned results, see "System Catalogs > System Views >PV_OS_RUN_INFO" in the Developer Guide.

Return type: record

get_instr_wait_event()

Description: obtains the waiting status and events of the current instance. For details about the returned results, see "System Catalogs > System Views > GS_WAIT_EVENTS" in the Developer Guide. If the GUC parameter enable_track_wait_event is off, this function returns 0.

Return type: record

pgxc_wait_events()

Description: queries statistics about waiting status and events on each node in a cluster. For details about the returned results, see "System Catalogs > System Views > PGXC_WAIT_EVENTS" in the Developer Guide. If the GUC parameter enable_track_wait_event is off, this function returns 0.

Return type: record

pgxc_stat_bgwriter()

Description: queries statistics about backend write processes on each node in a cluster. For details about the returned results, see "System Catalogs > System Views > PG_STAT_BGWRITER" in the Developer Guide.

Return type: record

pgxc_stat_replication()

Description: queries information about the log synchronization status on each node in a cluster, such as the location where the logs are sent and received. For details about the returned results, see "System Catalogs > System Views > PG_STAT_REPLICATION" in the Developer Guide.

Return type: record

pgxc_replication_slots()

Description: queries the replication status on each DN in a cluster. For details about the returned results, see "System Catalogs > System Views > PG_REPLICATION_SLOTS" in the Developer Guide.

Return type: record

pgxc_settings()

Description: queries information about runtime parameters on each node in a cluster. For details about the returned results, see "System Catalogs > System Views > PG_SETTINGS" in the Developer Guide.

Return type: record

pgxc_instance_time()

Description: queries the running time statistics of each node in a cluster and the time consumed in each execution phase. For details about the returned results, see "System Catalogs > System Views > PV_INSTANCE_TIME" in the Developer Guide.

Return type: record

pg_stat_get_redo_stat()

Description: queries Xlog redo statistics on the current node. For details about the returned results, see "System Catalogs > System Views > PV_REDO_STAT" in the Developer Guide.

Return type: record

pgxc_redo_stat()

Description: queries the Xlog redo statistics of each node in a cluster. For details about the returned results, see "System Catalogs > System Views > PV_REDO_STAT" in the Developer Guide.

Return type: record

get_local_rel_iostat()

Description: Obtains the disk I/O statistics of the current instance. For details about the returned results, see "System Catalogs > System Views > GS_REL_IOSTAT" in the Developer Guide.

Return type: record

pgxc_rel_iostat()

Description: queries the disk I/O statistics on each node in a cluster. For details about the returned result, see "System Catalogs > System Views > GS_REL_IOSTAT" in the Developer Guide.

Return type: record

get_node_stat_reset_time()

Description: Obtains the time when statistics of the current instance were reset.

Return type: timestamptz

pgxc_node_stat_reset_time()

Description: queries the time when the statistics of each node in a cluster are reset. For details about the returned result, see "System Catalogs > System Views > GS_NODE_STAT_RESET_TIME" in the Developer Guide.

Return type: record

When an instance is running, its statistics keep rising. In the following cases, the statistical values in the memory will be reset to 0:
  • The instance is restarted or a cluster switchover occurs.
  • The database is dropped.
  • A reset operation is performed. For example, the statistics counter in the database is reset using the pgstat_recv_resetcounter function or the Unique SQL statements are cleared using the reset_instr_unique_sql function.

If any of the preceding events occurs, GaussDB(DWS) will record the time when the statistics are reset. You can query the time using the get_node_stat_reset_time function.

pgxc_parallel_query(text, text)

Description: Runs a specified SQL query statement on a data instance of a specified type and returns the query result to the current CN. This function is supported in 8.1.2 or later.

The function has two parameters:

The first parameter specifies the instances on which the SQL statement is executed. Currently, the valid input parameters are dn, datanode, cn, coordinator, and all. Other values will cause function execution errors. dn and datanode indicate that the statement is executed on all DNs. cn and coordinator indicate that the statement is executed on all CNs. all indicates that the statement is executed on all CNs and DNs.

The second parameter specifies the verification of the objects queried by the SQL statement that is to be sent to a remote node for execution. User tables, distributed tables, and user-defined functions with multiple result sets are not supported.

Return type: record

  • This function is only used by developers to efficiently collect the execution information or status of instances in a cluster. You are not advised to use it directly.
  • This function contains multiple result sets, and the return data type is record. Therefore, you need to add the output column name and data type specified by the AS statement after the function call, as shown in the following: 
    SELECT * FROM pgxc_parallel_query('all', 'select node_name, db_name, thread_name, query_id, tid, lwtid, ptid, tlevel, smpid, wait_status, wait_event from pg_thread_wait_status') AS (node_name text, db_name text, thread_name text, query_id bigint, tid bigint, lwtid integer , ptid integer, tlevel integer , smpid integer, wait_status text, wait_event text);
  • The data type of the output result of the SQL statement specified by the second parameter of the function must be the same as the data type specified by the AS statement. Otherwise, an error may be reported during execution due to type mismatch.
  • The SQL statement specified by the second parameter of the function cannot trigger cross-node query. Otherwise, an error is reported.
  • The SQL statement specified by the second parameter of the function can only be a SELECT, UPDATE, DELETE, or INSERT statement.
    • The returning statement is not supported.
    • The user who invokes the function must have the operation permission on the SQL objects.
    • For INSERT statements, INSERT OVERWRITE, UPSERT, and INSERT INTO are not supported.
    • The UPDATE, DELETE, and INSERT statements can be executed only by the initial user in in-place upgrade mode or by the administrator in redistribution mode. The number of records modified by the statements on each instance must be the same. Otherwise, an error will be reported during statement execution. The function outputs a column of values of the bigint type. These values indicate the number of records operated by the statement on each instance. 
      SELECT * FROM pgxc_parallel_query('cn', 'UPDATE pg_partition SET relpages = 0') AS (updated bigint);

create_wdr_snapshot()

Description: Creates a performance data snapshot.

Return type: text

  • Only the database administrator SYSADMIN can execute this function.
  • This function can be executed only on CNs. If it is executed on DNs, the following message will be returned: "WDR snapshot can only be created on coordinator."
  • Before executing this function, ensure that the value of enable_wdr_snapshot is on. If its value is off, the following message will be returned for this function: "WDR snapshot request cannot be executed, because GUC parameter 'enable_wdr_snapshot' is off."
  • If the snapshot thread is not started for some reason, for example, the node is restarted, the following message will be returned for this function: "WDR snapshot request cannot be accepted, please retry later."
  • If this function fails to be executed, the following message will be returned: "Cannot respond to WDR snapshot request."
  • If this function is successfully executed, the following message will be returned: "WDR snapshot request has been submitted." This message indicates that the snapshot creation request has been sent to the background snapshot thread, but does not mean that the snapshot has been successfully created.

kill_snapshot(scope cstring)

Description: kills the background snapshot thread. This function sends a command to the background snapshot thread and waits for the thread to stop.

The input parameter scope indicates the operation scope. Its value can be local or global.

  • Value local indicates killing the snapshot thread on the current CN.
  • Value global indicates killing the snapshot thread on the current CN as well as those on all the other CNs in the cluster.
  • If any other value is passed, error message "Scope is invalid, use "local" or "global"." is displayed.
  • The input parameter can be left empty, in which case the default value local will be used.

Return type: none

  • Only the database administrator SYSADMIN can execute this function.
  • This function can be executed only on CNs. If it is executed on DNs, the following message will be returned: "kill_snapshot can only be executed on coordinator."
  • Executing this function sends a kill signal to the background snapshot thread and waits for it to finish. If the snapshot thread is not killed within 100s, the error message "Kill snapshot thread failed" is displayed.

generate_wdr_report(begin_snap_id bigint, end_snap_id bigint, report_type cstring, report_scope cstring, node_name cstring)

Description: Creates a load analysis report.

The input parameters are described as follows:

  • begin_snap_id and end_snap_id: IDs of the start and end snapshots, respectively. The IDs are of the bigint type. The value of begin_snap_id must be less than that of end_snap_id, and the time for the start and end snapshots cannot overlap. You can check whether the snapshot time overlaps by querying select s1.end_ts < s2.start_ts from (select * from dbms_om.snapshot where snapshot_id=end_snap_id) as s2; in the dbms_om.snapshot table. If true is returned, the snapshot time does not overlap. Otherwise, the snapshot time overlaps.
  • report_type: report type. The value is a cstring and can be summary, detail, or all.
  • report_scope: report scope. The value is a cstring and can be cluster or node.
  • node_name: node name. The value is a cstring. If report_scope is node, the value of this parameter must be pg_catalog, which indicates the CN or DN name in the node_name column of the pgxc_node table.
Return type: text
  • Only the database administrator SYSADMIN can execute this function.
  • This function can be executed only on CNs. If it is executed on DNs, the following message will be returned: "WDR report can only be created on coordinator."
  • If the report is created successfully, message "Report %s has been generated" will be returned.
  • The statistics cannot be reset between the time the start snapshot is taken and the time the end snapshot is taken. Otherwise, error message "Instance reset time is different" will be displayed. For details about the events that cause a statistics reset, see the pgxc_node_stat_reset_time function.

wdr_xdb_query(db_name text, snapshot_id bigint, view_name text)

Description: Queries a specified view in a specified database. The query results of some views vary depending on databases. For example, the global_table_stat view is used to query the statistics of a table. The results of querying this view vary because tables in different databases are different. The wdr_xdb_query function can access the database specified by db_name in the current connection and query the view specified by view_name in the database. The input parameters are described as follows:

  • db_name: specifies the name of a database. The value is of the text type.
  • snapshot_id: specifies the snapshot ID. The value is of the bigint type. For details, see "Performance View Snapshot".
  • view_name: specifies the name of a view. The value is of the text type. The view name must be in the following whitelist:
    • global_table_stat
    • global_table_change_stat
    • global_column_table_io_stat
    • global_row_table_io_stat

      The return value type is record. The first column is snapshot_id bigint, and the second column is db_name text. The names, types, and sequences of other columns are the same as those of the views specified by view_name.

      Example:

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      select snapshot_id, db_name, schemaname, relname, distribute_mode, seq_scan ,seq_tuple_read ,index_scan ,index_tuple_read ,tuple_inserted
,tuple_updated ,tuple_deleted ,tuple_hot_updated ,live_tuples ,dead_tuples from wdr_xdb_query('postgres'::text, 1, 'global_table_stat'::text) as i(snapshot_id bigint, db_name text, schemaname name, relname name, distribute_mode char, seq_scan bigint, seq_tuple_read bigint, index_scan bigint, index_tuple_read bigint, tuple_inserted bigint, tuple_updated bigint, tuplee_deleted bigint, tuple_hot_updated bigint, live_tuples bigint, dead_tuples bigint);
      • This function is supported only in 8.1.2 or later.
      • Only the database administrator SYSADMIN can execute this function.
      • This function can be used to query only the views in the whitelist. If you use this function to query other views, the error message Input view name is invalid. will be displayed.

vac_fileclear_relation(oid)

Description: Forcibly clears VACUUM rewritten files in a specified column-store table to reclaim space.

Parameter: OID of a column-store table.

Return type: integer

  • Before using this function, set colvacuum_threshold_scale_factor and ensure that the files are cleared and space reclaimed only after the VACUUM process has rewritten the files of the specified column-store table.
  • This function exclusively locks a specified column-store table.

vac_fileclear_all_relation()

Description: Forcibly clears VACUUM rewritten files in all specified column-store tables to reclaim space.

Return type: record

get_col_file_info(table_name)

Description: Queries the number of empty CU files and the total number of CU files in a specified column-store table. This function is supported only in cluster 8.2.0 and later versions.

Parameter: Name of a column-store table.

Return type: int

Fields in the returned value:

  • total_file_num int: total number of CU files. The value ranges from -1 to INT_MAX. -1 indicates a failure, which could be caused by unsupported table types. The values in the range 0 to INT_MAX indicates the total number of files.
  • empty_file_num int: number of empty CU files. The value ranges from -1 to INT_MAX. -1 indicates a failure, which could be caused by unsupported table types. The values in the range 0 to INT_MAX indicates the total number of empty files.

Example:

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call get_col_file_info('t4');
 total_file_num | empty_file_num
----------------+----------------
             10 |              7
(1 row)

get_all_col_file_info()

Description: Queries the number of empty CU files and the total number of CU files in all column-store tables. This function is supported only in cluster 8.2.0 and later versions.

Return type: record

Fields in the returned value:

  • space_name text: schema to which the column-store tables belong
  • table_name text: name of a column-store table
  • total_file_num int: total number of CU files. The value ranges from -1 to INT_MAX. -1 indicates a failure, which could be caused by unsupported table types. The values in the range 0 to INT_MAX indicates the total number of files.
  • empty_file_num int: number of empty CU files. The value ranges from -1 to INT_MAX. -1 indicates a failure, which could be caused by unsupported table types. The values in the range 0 to INT_MAX indicates the total number of empty files.

Example:

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call get_all_col_file_info();
 space_name | table_name | total_file_num | empty_file_num
------------+------------+----------------+----------------
 public     | t4         |             10 |              7
 public     | t2         |              1 |              1
 public     | t1         |              3 |              0
(3 rows)

pg_get_bucket_epoch(relid)

Description: Queries the epoch value of the v3 table on the current node. To print the epoch values of all subpartitions in a partitioned table, you must provide the OID of the parent table. This function can be executed only in VW write scenarios. This function is supported only by clusters of version 9.1.0.200 or later.

Return type: record

Fields in the returned value:

  • relfilenode oid: column-store relfilenode of a non-partitioned table. For a partitioned table, the value is 0.
  • partfilenode oid: relfilenode of a column-store partitioned table. For a non-partitioned table, the value is 0.
  • epoch xid: epoch value corresponding to the table on the current node.

Example:

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select * from pg_get_bucket_epoch(2147483732);
 relfilenode | partfilenode |  epoch
-------------+--------------+--------
  2137383742 |            0 | 1000001
(1 row)

pg_get_bucket_epoch(tablespaceid, databaseid, relfilenode)

Description: Queries the epoch value of the v3 table on the current node. Enter the OID of the tablespace where the v3 table is located, the OID of the database, and the relfilenode corresponding to the table. This function can be executed in both VW write and read scenarios. This function is supported only by clusters of version 9.1.0.200 or later.

Return type: xid

Fields in the returned value:

epoch xid: epoch value corresponding to the table on the current node.

Example:

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select * from pg_get_bucket_epoch(2147483729, 16792, 2147483732);
 epoch
-------
1000001
(1 row)

pgxc_get_bucket_epoch(tablespaceid, databaseid, relfilenode)

Description: Queries the epoch values of the v3 table on all DNs. Enter the OID of the tablespace where the v3 table is located, the OID of the database, and the relfilenode corresponding to the table. This function can be executed in both VW write and read scenarios. This function is supported only by clusters of version 9.1.0.200 or later.

Return type: record

Fields in the returned value:

  • nodename text: node name
  • epoch xid: epoch value corresponding to the table on the current node.

Example:

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select * from pgxc_get_bucket_epoch(2147483729, 16792, 2147483732);
  nodename |  epoch
-----------+---------
 datanode3 | 1000001
 datanode1 |       0
 datanode2 |       0
(1 row)

get_volatile_pg_class()

Description: Obtains the pg_class metadata related to all volatile temporary tables in the current session. This parameter is supported by version 8.2.0 or later clusters.

Return type: record

Fields in the returned value:

  • oid: OID of the volatile temporary table.
  • Other fields: same as the fields (excluding hidden fields) in the pg_class system catalog.

get_volatile_pg_class(relname text)

Description: Obtains the pg_class metadata related to a specified volatile temporary table in the current session. This parameter is supported by version 8.2.0 or later clusters.

Parameter: name of the volatile temporary table in the current session.

Return type: record

Fields in the returned value:

  • oid: OID of the volatile temporary table.
  • Other fields: same as the fields (excluding hidden fields) in the pg_class system catalog.

Example:

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SELECT * FROM get_volatile_pg_class('tx1');
  oid  | relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace | relpages | reltuples | relallvisible | reltoastrelid | reltoastidxid | reldeltarelid |
 reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassub
class | relcmprs | relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl |            reloptions            | relreplident | relfrozenxid64
-------+---------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+---------------+---------------+---------------+---------------+
-------------+----------------+--------------+-------------+-------------+----------------+---------+----------+-----------+------------+------------+-------------+----------------+----------
------+----------+------------------+----------------+----------+--------------+--------+----------------------------------+--------------+----------------
 16772 | tx1     |        16770 |   16774 |         0 |       10 |     0 |       16772 |          1665 |        0 |         0 |             0 |         16775 |             0 |             0 |
           0 |              0 |            0 | f           | f           | v              | r       |        2 |         0 | f          | f          | f           | f              | f
      | 1        | f                | f              | n        | 11815        |        | {orientation=row,compression=no} | d            |          11815
(1 row)

get_volatile_pg_attribute()

Description: Obtains the pg_attribute metadata related to all volatile temporary tables in the current session. This parameter is supported by version 8.2.0 or later clusters.

Return type: record

Fields in the returned value:
  • oid: OID of the column.
  • Other fields: same as the fields (excluding hidden fields) in the pg_attribute catalog.

get_volatile_pg_attribute(relname text, attrname text)

Description: Obtains the pg_attribute metadata related to a specified volatile temporary table in the current session. This parameter is supported by version 8.2.0 or later clusters.

Parameter:

  • relname: table name (must be in the current session).
  • attrname: column name.

Return type: record

Fields in the returned value:

  • oid: OID of the column.
  • Other fields: same as the fields (excluding hidden fields) in the pg_attribute catalog.

Example:

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SELECT * FROM get_volatile_pg_attribute('tx1', 'b');
 attrelid | attname | atttypid | attstattarget | attlen | attnum | attndims | attcacheoff | atttypmod | attbyval | attstorage | attalign | attnotnull | atthasdef | attisdropped | attislocal |
 attcmprmode | attinhcount | attcollation | attacl | attoptions | attfdwoptions | attinitdefval | attkvtype
----------+---------+----------+---------------+--------+--------+----------+-------------+-----------+----------+------------+----------+------------+-----------+--------------+------------+
-------------+-------------+--------------+--------+------------+---------------+---------------+-----------
    16772 | b       |       25 |            -1 |     -1 |      2 |        0 |          -1 |        -1 | f        | x          | i        | f          | f         | f            | t          |
 127         |           0 |          100 |        |            |               |               | 0
(1 row)

pg_get_publication_tables(pubname text)

Description: Returns the relid list of tables to be published based on the publication name. This function is supported by version 8.2.0.100 or later clusters.

Parameter: pubname

Return type: set of OID

Example:

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SELECT * FROM pg_get_publication_tables('mypub');
 relid 
-------
 16757
 16776
(2 rows)

pg_relation_is_publishable(relname regclass)

Description: Checks whether a table can be published. This function is supported by version 8.2.0.100 or later clusters.

Parameter: relname

Return type: Boolean

Example:

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SELECT * FROM pg_relation_is_publishable('t1');
 pg_relation_is_publishable 
----------------------------
 t
(1 row)

get_col_cu_info(schema_name text, table_name text, row_count int8, dirty_percent int8)

Description: Queries the CU information of a column-store table. The CU information of each partition is collected separately. This function is supported by version 8.2.0.100 or later clusters.

Parameters: schema name (mandatory), table name (mandatory), threshold for the number of rows in a small CU (optional, 200 by default, ranging from 1 to 60000, and percentage threshold for deleting dirty CUs (optional, 70 by default, ranging from 1 to 100)

Return type: record

Fields in the returned value:

node_name: DN name.

part_name: partition name. This column is empty for a common table.

zero_size_cu_count: number of CUs whose cuSize is 0 and number of rows is less than or equal to row_count.

small_cu_count: number of CUs whose cuSize is ALIGNOF_CUSIZE(8192) and number of rows is less than or equal to row_count.

dirty_cu_count: number of CUs whose deadtupe percentage exceeds dirty_percent due to deletion.

total_cu_count: total number of CUs.

small_cu_size: total size of 8 KB CUs.

total_cu_size: total CU size.

Example:

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 SELECT * FROM get_col_cu_info('public','hs_part');
 node_name | part_name | zero_size_cu_count | small_cu_count | dirty_cu_count | total_cu_count | small_cu_size | total_cu_size
-----------+-----------+--------------------+----------------+----------------+----------------+---------------+---------------
 dn_1      | p1        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
 dn_1      | p2        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
 dn_1      | p3        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
(3 rows)

 SELECT * FROM get_col_cu_info('public','hs_part', 200, 90);
 node_name | part_name | zero_size_cu_count | small_cu_count | dirty_cu_count | total_cu_count | small_cu_size | total_cu_size
-----------+-----------+--------------------+----------------+----------------+----------------+---------------+---------------
 dn_1      | p1        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
 dn_1      | p2        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
 dn_1      | p3        |                  3 |              0 |              0 |              3 | 0 bytes       | 0 bytes
(3 rows)

get_col_file_vacuum_info(schema_name text, table_name text, force_get_rewritten_file_num bool)

Description: Queries the vacuum information of a column-store table. The vacuum information of each partition is collected separately. This function is supported by version 8.2.0.100 or later clusters.

Parameters: schema name (mandatory), table name (mandatory), and whether to forcibly obtain the precise number of files that can be cleared (mandatory, false by default)

Return type: record

Fields in the returned value:

node_name: DN name.

part_name: partition name. This column is empty for a common table.

total_file_num: total number of CU files.

rewritable_file_num: number of files that can be rewritten but have not been rewritten.

rewritten_file_num: number of files that have been rewritten but have not been cleared. The value is obtained from data in the memory. If the memory data is lost due to reasons such as restart, you can set force_get_rewritten_file_num=true to forcibly obtain the accurate number of files that can be cleared.

empty_file_num: number of cleared files.

Example:

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SELECT * FROM get_col_file_vacuum_info('public','pa',false);
 node_name | part_name | total_file_num | rewritable_file_num | rewritten_file_num | empty_file_num
-----------+-----------+----------------+---------------------+--------------------+----------------
 datanode1 | pa1       |              1 |                   0 |                  0 |              0
 datanode1 | pa2       |              1 |                   0 |                  0 |              0
 datanode2 | pa1       |              1 |                   0 |                  0 |              0
 datanode2 | pa2       |              1 |                   0 |                  0 |              0
 datanode3 | pa1       |              1 |                   0 |                  0 |              0
 datanode3 | pa2       |              1 |                   0 |                  0 |              0
(6 rows)

get_col_file_vacuum_info(schema_name text, table_name text, colvacuum_threshold_scale_factor int)

Description: Queries the vacuum information of a column-store table. The vacuum information of each partition is collected separately. This function is supported by version 8.2.0.100 or later clusters.

Parameters: schema name (mandatory), table name (mandatory), and colvacuum_threshold_scale_factor (mandatory. The value range is 0 to 100, indicating the ratio of dead tuples.)

Return type: record

Return value:

node_name: DN name.

part_name: partition name. This column is empty for a common table.

total_file_num: total number of CU files.

rewritable_file_num: number of files that can be rewritten but have not been rewritten.

rewritten_file_num: number of files that have been rewritten but have not been cleared. The value is obtained from data in the memory. If the memory data is lost due to reasons such as restart, you can set force_get_rewritten_file_num=true to forcibly obtain the accurate number of files that can be cleared.

empty_file_num: number of cleared files.

Example:

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SELECT * FROM get_col_file_vacuum_info('public','pa',10);
 node_name | part_name | total_file_num | rewritable_file_num | rewritten_file_num | empty_file_num
-----------+-----------+----------------+---------------------+--------------------+----------------
 datanode1 | pa1       |              1 |                   0 |                  0 |              0
 datanode1 | pa2       |              1 |                   0 |                  0 |              0
 datanode2 | pa1       |              1 |                   0 |                  0 |              0
 datanode2 | pa2       |              1 |                   0 |                  0 |              0
 datanode3 | pa1       |              1 |                   0 |                  0 |              0
 datanode3 | pa2       |              1 |                   0 |                  0 |              0
(6 rows)

get_all_col_cu_info(row_count int8)

Description: Queries the CU information of all column-store tables in the database. This function is supported by version 8.2.0.100 or later clusters.

Parameter: threshold for the number of rows in a small CU (optional, 200 by default, and ranging from 1 to 60000)

Return type: record

Fields in the returned value:

node_name: DN name.

schema_name: schema name.

table_name: table name.

zero_size_cu_count: number of CUs whose cuSize is 0 and number of rows is less than or equal to row_count.

small_cu_count: number of CUs whose cuSize is ALIGNOF_CUSIZE(8192) and number of rows is less than or equal to row_count.

total_cu_count: total number of CUs.

small_cu_size: total size of 8 KB CUs.

total_cu_size: total CU size.

Example:

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SELECT * FROM get_all_col_cu_info(200);
 node_name | schema_name |      table_name      | zero_size_cu_count | small_cu_count | total_cu_count | small_cu_size | total_cu_size
-----------+-------------+----------------------+--------------------+----------------+----------------+---------------+---------------
 datanode1 | public      | udi_48076            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
 datanode1 | public      | udi_48077            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
 datanode2 | public      | udi_48076            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
 datanode2 | public      | udi_48077            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
 datanode3 | public      | udi_48076            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
 datanode3 | public      | udi_48077            |                  5 |              1 |              6 | 8192 bytes    | 8192 bytes
(6 rows)

get_all_col_file_vacuum_info(force_get_rewritten_file_num bool)

Description: Queries the vacuum information of all column-store tables in the database. This function is supported by version 8.2.0.100 or later clusters.

Parameter: whether to forcibly obtain the accurate number of files that can be cleared (mandatory. It can be true or false .)

Return type: record

Fields in the returned value:

node_name: DN name.

schema_name: schema name.

table_name: table name.

total_file_num: total number of CU files.

rewritable_file_num: number of files that can be rewritten but have not been rewritten.

rewritten_file_num: number of files that have been rewritten but have not been cleared. The value is obtained from data in the memory. If the memory data is lost due to reasons such as restart, you can set force_get_rewritten_file_num=true to forcibly obtain the accurate number of files that can be cleared.

empty_file_num: number of cleared files.

Example:

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SELECT * FROM get_all_col_file_vacuum_info(false);
 node_name | schema_name |      table_name      | total_file_num | rewritable_file_num | rewritten_file_num | empty_file_num
-----------+-------------+----------------------+----------------+---------------------+--------------------+----------------
 datanode1 | public      | udi_57373            |              2 |                   0 |                  0 |              1
 datanode1 | public      | udi_57374            |              2 |                   0 |                  0 |              1
 datanode2 | public      | udi_57373            |              2 |                   0 |                  0 |              1
 datanode2 | public      | udi_57374            |              2 |                   0 |                  0 |              1
 datanode3 | public      | udi_57373            |              2 |                   0 |                  0 |              1
 datanode3 | public      | udi_57374            |              2 |                   0 |                  0 |              1

show_tsc_info()

Description: Queries the TimeStamp-Counter (TSC) information obtained from the current database node. This function is supported by version 8.2.1 or later clusters.

Return type: record

Table 4 Parameter

Name

Type

Description

node_name

text

Node name

tsc_mult

bigint

TSC conversion multiplier

tsc_shift

bigint

TSC conversion shifts

tsc_frequency

float8

TSC frequency.

tsc_use_freqency

boolean

Indicates whether to use the TSC frequency for time conversion.

tsc_ready

boolean

Indicates whether the TSC frequency can be used for time conversion

tsc_scalar_error_info

text

Error information about obtaining TSC conversion information

tsc_freq_error_info

text

Error information about obtaining TSC frequency information

Example:

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SELECT * FROM show_tsc_info();  
  node_name   | tsc_mult | tsc_shift | tsc_frequency | tsc_use_frequency | tsc_ready |     tsc_scalar_error_info     | tsc_freq_error_info
--------------+----------+-----------+---------------+-------------------+-----------+-------------------------------+---------------------
 coordinator1 |          |           |          2400 | t                 | t         | TSC scalar is not initialized |

get_tsc_info()

Description: Re-obtains the TimeStamp-Counter (TSC) information of the current database node. This function is supported by version 8.2.1 or later clusters.

Return type: record

Table 5 show_tsc_info() return columns

Column

Type

Description

node_name

text

Node name

tsc_mult

bigint

TSC conversion multiplier

tsc_shift

bigint

TSC conversion shifts

tsc_frequency

float8

TSC frequency

tsc_use_freqency

boolean

Indicates whether to use the TSC frequency for time conversion.

tsc_ready

boolean

Indicates whether the TSC frequency can be used for time conversion

tsc_scalar_error_info

text

Error information about obtaining TSC conversion information

tsc_freq_error_info

text

Error information about obtaining TSC frequency information

Example:

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SELECT * FROM get_tsc_info();  
  node_name   | tsc_mult | tsc_shift | tsc_frequency | tsc_use_frequency | tsc_ready |     tsc_scalar_error_info     | tsc_freq_error_info
--------------+----------+-----------+---------------+-------------------+-----------+-------------------------------+---------------------
 coordinator1 |          |           |          2400 | t                 | t         | TSC scalar is not initialized |

test_tsc_info(time float8, loops int)

Description: Tests the accuracy of the time converted using the TimeStamp-Counter (TSC) on the current node. This function is supported by version 8.2.1 or later clusters.

The input parameters are described as follows:

  • time: indicates the test time difference (unit: s). The test duration must be less than or equal to 60s.
  • loops: indicates the number of tests. The value ranges from 1 to 10.

Return type: record

Fields in the returned value:

  • id: number of cycles.
  • real_time_diff: time difference obtained using gettimeofday (unit: us).
  • est_time_scalar: time difference (unit: μs) converted using TSC conversion information.
  • est_time_frequency: time difference (unit: μs) converted using the TSC frequency.

Example:

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SELECT * FROM test_tsc_info(0.01,10);
 id | real_time_diff | est_time_scalar | est_time_frequency
----+----------------+-----------------+--------------------
  1 |          10057 |                 |            10056.9
  2 |          10057 |                 |   10057.4816666667
  3 |          10056 |                 |   10055.2841666667
  4 |          10054 |                 |   10054.4908333333
  5 |          10055 |                 |         10054.2875
  6 |          10055 |                 |   10054.7483333333
  7 |          10055 |                 |         10054.4725
  8 |          10054 |                 |   10054.0766666667
  9 |          10058 |                 |   10058.1016666667
 10 |          10057 |                 |   10056.3733333333
(10 rows)