openGauss routine maintenance: slow sql diagnosis
Tags: opengauss
Published: 2023-03-22 03:25:57

Slow sql diagnosis
Background Information
When the SQL statement execution performance does not meet expectations, you can view the SQL statement execution information, which is convenient for analyzing the behavior of the SQL statement execution and diagnosing problems related to the SQL statement execution.

prerequisite
The database instance is running fine.
To query SQL statement information, you need to set the GUC parameter track_stmt_stat_level reasonably. The track_stmt_stat_level parameter controls the level of statement execution tracking. The first part controls full SQL, and the second part controls slow SQL. For slow SQL, when the value of track_stmt_stat_level is not OFF, and the SQL execution time exceeds log_min_duration_statement, it will be recorded as slow SQL. The default value is "OFF,L0", and it is recommended to set it to "L0,L0".
It can only be operated with system administrator and monitoring administrator privileges.
执行命令查看数据库实例中SQL语句执行信息
select * from dbe_perf.get_global_full_sql_by_timestamp(start_timestamp, end_timestamp); 
例如：
select * from DBE_PERF.get_global_full_sql_by_timestamp('2020-12-01 09:25:22', '2020-12-31 23:54:41');
-[ RECORD 1 ]--------+---------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------
node_name            | dn_6001_6002_6003
db_name              | postgres
schema_name          | "$user",public
origin_node          | 1938253334
user_name            | user_dj
application_name     | gsql
client_addr          |
client_port          | -1
unique_query_id      | 3671179229
debug_query_id       | 72339069014839210
query                | select name, setting from pg_settings where name in (?)
start_time           | 2020-12-19 16:19:51.216818+08
finish_time          | 2020-12-19 16:19:51.224513+08
slow_sql_threshold   | 1800000000
transaction_id       | 0
thread_id            | 139884662093568
session_id           | 139884662093568
n_soft_parse         | 0
n_hard_parse         | 1
query_plan           | Datanode Name: dn_6001_6002_6003
                     | Function Scan on pg_show_all_settings a  (cost=0.00..12.50 rows=5 width=64)
                     |   Filter: (name = '***'::text)
...

执行命令查看数据库实例中慢SQL语句执行信息
select * from dbe_perf.get_global_slow_sql_by_timestamp(start_timestamp, end_timestamp);
例如：
select * from DBE_PERF.get_global_slow_sql_by_timestamp('2020-12-01 09:25:22', '2020-12-31 23:54:41');
-[ RECORD 1 ]--------+---------------------------------------------------------------------------------------------------
node_name            | dn_6001_6002_6003
db_name              | postgres
schema_name          | "$user",public
origin_node          | 1938253334
user_name            | user_dj
application_name     | gsql
client_addr          |
client_port          | -1
unique_query_id      | 2165004317
debug_query_id       | 72339069014839319
query                | select * from DBE_PERF.get_global_slow_sql_by_timestamp(?, ?);
start_time           | 2020-12-19 16:23:20.738491+08
finish_time          | 2020-12-19 16:23:20.773714+08
slow_sql_threshold   | 10000
transaction_id       | 0
thread_id            | 139884662093568
session_id           | 139884662093568
n_soft_parse         | 10
n_hard_parse         | 8
query_plan           | Datanode Name: dn_6001_6002_6003
                     | Result  (cost=1.01..1.02 rows=1 width=0)
                     |   InitPlan 1 (returns $0)
                     |     ->  Seq Scan on pgxc_node  (cost=0.00..1.01 rows=1 width=64)
                     |           Filter: (nodeis_active AND ((node_type = '***'::"char") OR (node_type = '***'::"char")))
...

查看当前主节点SQL语句执行信息
select * from statement_history;
例如：
select * from statement_history;
-[ RECORD 1 ]--------+---------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------
db_name              | postgres
schema_name          | "$user",public
origin_node          | 1938253334
user_name            | user_dj
application_name     | gsql
client_addr          |
client_port          | -1
unique_query_id      | 3671179229
debug_query_id       | 72339069014839210
query                | select name, setting from pg_settings where name in (?)
start_time           | 2020-12-19 16:19:51.216818+08
finish_time          | 2020-12-19 16:19:51.224513+08
slow_sql_threshold   | 1800000000
transaction_id       | 0
thread_id            | 139884662093568
session_id           | 139884662093568
n_soft_parse         | 0
n_hard_parse         | 1
query_plan           | Datanode Name: dn_6001_6002_6003
                     | Function Scan on pg_show_all_settings a  (cost=0.00..12.50 rows=5 width=64)
                     |   Filter: (name = '***'::text)
...

查看当前备节点SQL语句执行信息
select * from dbe_perf.standby_statement_history(is_only_slow, start_timestamp, end_timestamp);
例如：
select * from dbe_perf.standby_statement_history(true, '2022-08-01 09:25:22', '2022-08-31 23:54:41');
db_name              | postgres
schema_name          | "$user",public
origin_node          | 0
user_name            | user_dj
application_name     | gsql
client_addr          |
client_port          | -1
unique_query_id      | 1660376009
debug_query_id       | 281474976710740
query                | select name, setting from pg_settings where name in (?)
start_time           | 2022-08-19 16:19:51.216818+08
finish_time          | 2022-08-19 16:19:51.224513+08
slow_sql_threshold   | 1800000000
transaction_id       | 0
thread_id            | 140058747205376
session_id           | 140058747205376
n_soft_parse         | 0
n_hard_parse         | 1
query_plan           | Datanode Name: sgnode
                     | Function Scan on pg_show_all_settings a  (cost=0.00..12.50 rows=5 width=64)
                     |   Filter: (name = '***'::text)
...