Other Functions

pgxc_pool_check()
Description: Checks whether the connection data buffered in the pool is consistent with pgxc_node.

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.

select table_skewness('tx','a');
 table_skewness 
----------------
 (1,7,70.000%)
 (2,2,20.000%)
 (0,1,10.000%)
(3 rows)

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 the columns in the tx table.

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.
- 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.

pgxc_get_stat_dirty_tables(int dirty_percent, int n_tuples)

Description: Obtains information about insertion, update, and deletion operations on tables and the dirty page rate of tables. This function optimizes the performance of the PGXC_GET_STAT_ALL_TABLES view. It can quickly filter out tables whose dirty page rate is greater than dirty_percent and number of dead tuples is greater than n_tuples.

Return type: SETOF record

The following table describes return columns.

Name	Type	Description
relid	oid	Table OID
relname	name	Table name
schemaname	name	Schema name of the table
n_tup_ins	bigint	Number of inserted tuples
n_tup_upd	bigint	Number of updated tuples
n_tup_del	bigint	Number of deleted tuples
n_live_tup	bigint	Number of live tuples
n_dead_tup	bigint	Number of dead tuples
dirty_page_rate	numeric(5,2)	Dirty page rate (%) of a table

pgxc_get_stat_dirty_tables(int dirty_percent, int n_tuples, text schema)
Description: Obtains information about insertion, update, and deletion operations on tables and the dirty page rate of tables. This function can quickly filter out tables whose dirty page rate is greater than page_dirty_rate, number of dead tuples is greater than n_tuples, and schema name is schema.

Return type: SETOF record

The return columns of the function are the same as those of the pgxc_get_stat_dirty_tables(int dirty_percent, int n_tuples) function.
plan_seed()
Description: Obtains the seed value of the previous query statement (internal use).

Return type: int
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 GS_INSTR_UNIQUE_SQL.

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: int

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 1.
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 1** 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	character varying	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

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 deleted.
- 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.