Real-time TopSQL

You can query real-time Top SQL in real-time resource monitoring views at different levels. The real-time resource monitoring view records the resource usage (including memory, disk, CPU time, and I/O) and performance alarm information during job running.

The following table describes the external interfaces of the real-time views.

**Table 1** Real-time resource monitoring views
Level	Monitored Node	View
Query level/perf level	Current CN	GS_WLM_SESSION_STATISTICS
Query level/perf level	All CNs	PGXC_WLM_SESSION_STATISTICS
Operator level	Current CN	GS_WLM_OPERATOR_STATISTICS
Operator level	All CNs	PGXC_WLM_OPERATOR_STATISTICS

The view level is determined by the resource monitoring level, that is, the resource_track_level configuration.
The perf and operator levels affect the values of the query_plan and warning columns in GS_WLM_SESSION_STATISTICS/PGXC_WLM_SESSION_INFO. For details, see SQL Self-Diagnosis.
Prefixes gs and pgxc indicate views showing single CN information and those showing cluster information, respectively. Common users can log in to a CN in the cluster to query only views with the gs prefix.
When you query this type of views, there will be network latency, because the views obtain resource usage in real time.
If instance fault occurs, some SQL statement information may fail to be recorded in real-time resource monitoring views.
SQL statements are recorded in real-time resource monitoring views as follows:
- DDL statements are not recorded, such as the execution of CREATE, ALTER, DROP, GRANT, REVOKE, and VACUUM statements.
- DML statements are recorded, including:
  - the execution of SELECT, INSERT, UPDATE, and DELETE
  - the execution of EXPLAIN ANALYZE and EXPLAIN PERFORMANCE
  - the use of a query-level/perf-level view, which also supports the CREATE TABLE AS syntax.
- Statements in functions and stored procedures and statements used for calling functions and stored procedures are recorded. Statements in loop bodies (if any) of functions and stored procedures are not recorded.
- Statements in anonymous blocks are not recorded.
- Statements in transaction blocks are recorded. Statements in loop bodies (if any) of transaction blocks are not recorded.
- Cursor statements are recorded.
- Jobs in a redistribution process are not monitored.

Prerequisites

The GUC parameter enable_resource_track is set to on. The default value is on.
The GUC parameter resource_track_level is set to query, perf, or operator. The default value is query.
Job monitoring rules are as follows:
- Jobs whose execution cost estimated by the optimizer is greater than or equal to resource_track_cost.
- Long query jobs
If the Cgroups function is properly loaded, you can run the gs_cgroup -P command to view information about Cgroups.

In the preceding prerequisites, enable_resource_track is a system-level parameter that specifies whether to enable resource monitoring. resource_track_level is a session-level parameter. You can set the resource monitoring level of a session as needed. The following table describes the values of the two parameters.

**Table 2** Setting the resource monitoring level to collect statistics
enable_resource_track	resource_track_level	Query-Level Information	Operator-Level Information
on(default)	none	Not collected	Not collected
	query(default)	Collected	Not collected
	perf	Collected	Not collected
	operator	Collected	Collected
off	none/query/operator	Not collected	Not collected

Procedure

Query for the real-time CPU information in the gs_session_cpu_statistics view.
1

SELECT * FROM gs_session_cpu_statistics;
Query for the real-time memory information in the gs_session_memory_statistics view.
1

SELECT * FROM gs_session_memory_statistics;
Query for the real-time resource information about the current CN in the gs_wlm_session_statistics view.
1

SELECT * FROM gs_wlm_session_statistics;
Query for the real-time resource information about all CNs in the pgxc_wlm_session_statistics view.
1

SELECT * FROM pgxc_wlm_session_statistics;
Query for the real-time resource information about job operators on the current CN in the gs_wlm_operator_statistics view.
1

SELECT * FROM gs_wlm_operator_statistics;
Query for the real-time resource information about job operators on all CNs in the pgxc_wlm_operator_statistics view.
1

SELECT * FROM pgxc_wlm_operator_statistics;
Query for the load management information about the jobs executed by the current user in the PG_SESSION_WLMSTAT view.
1

SELECT * FROM pg_session_wlmstat;
Query the job execution status of the current user on each CN in the pgxc_wlm_workload_records view (this view is available when the dynamic load function is enabled, that is, enable_dynamic_workload is set to on).
1

SELECT * FROM pgxc_wlm_workload_records;