慢SQL诊断
背景信息
在SQL语句执行性能不符合预期时，可以查看SQL语句执行信息，便于事后分析SQL语句执行时的行为，从而诊断SQL语句执行出现的相关问题。
前提条件
- 数据库实例运行正常。
- 查询SQL语句信息，需要正确设置GUC参数track_stmt_stat_level。
- 只能用系统管理员和监控管理员权限进行操作。
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)
...