pg_stat_activity 視圖的每一行與每一個服務器進程一一對應，顯示與該進程當前活動相關的信息。

pg_cancel_backend和pg_terminate_backend服務器信號函數
pg_cancel_backend(pid ? int): 取消一個后端的當前查詢。如果調用角色是被取消后端的擁有者角色的成員或者調用角色已經被授予pg_signal_backend，這也是允許的，不過只有超級用戶才能取消超級用戶的后端。?
pg_terminate_backend(pid int):
中止一個后端。如果調用角色是被取消后端的擁有者角色的成員或者調用角色已經被授予pg_signal_backend，這也是允許的，不過只有超級用戶才能取消超級用戶的后端。
這兩個函數的區別在于：pg_cancel_backend 只是取消當前某一個進程的查詢操作，但不能釋放數據庫連接。但pg_terminate_backend 可以在pg的后臺殺死這個進程，從而釋放出寶貴的連接資源。
?

-- 1) 當前會話

postgres=# SELECT COUNT(*) FROM pg_stat_activity;count -------12 (1 row)postgres=# SELECT datname,pid,state,backend_type FROM pg_stat_activity;datname | pid | state | backend_type -----------+-------+--------+------------------------------| 23635 | | logical replication launcher| 23633 | | autovacuum launcherpostgres | 63810 | active | client backendpostgres | 60710 | idle | client backendpostgres | 59702 | idle | client backendzoo | 59736 | idle | client backendsample_db | 59772 | idle | client backendzoo | 59972 | idle | client backendzoo | 60011 | idle | client backend| 23631 | | background writer| 23630 | | checkpointer

-- 2) 用pg_cancel_backend函數殺會話(其中的pid為60011和59972)
?

postgres=# SELECT pg_cancel_backend(60011);pg_cancel_backend -------------------t (1 row)postgres=# SELECT pg_terminate_backend(59972);pg_terminate_backend ----------------------t (1 row)postgres=# SELECT datname,pid,state,backend_type FROM pg_stat_activity;datname | pid | state | backend_type -----------+-------+--------+------------------------------| 23635 | | logical replication launcher| 23633 | | autovacuum launcherpostgres | 63810 | active | client backendpostgres | 60710 | idle | client backendpostgres | 59702 | idle | client backendzoo | 59736 | idle | client backendsample_db | 59772 | idle | client backendzoo | 60011 | idle | client backend| 23631 | | background writer| 23630 | | checkpointer| 23632 | | walwriter (11 rows)---- 發現pid59972會話殺掉了但pid60011沒有殺掉，再執行一遍，發現還是沒殺掉該會話 postgres=# SELECT pg_cancel_backend(60011);pg_cancel_backend -------------------t (1 row)postgres=# SELECT datname,pid,state,backend_type FROM pg_stat_activity;datname | pid | state | backend_type -----------+-------+--------+------------------------------| 23635 | | logical replication launcher| 23633 | | autovacuum launcherpostgres | 63810 | active | client backendpostgres | 60710 | idle | client backendpostgres | 59702 | idle | client backendzoo | 59736 | idle | client backendsample_db | 59772 | idle | client backendzoo | 60011 | idle | client backend| 23631 | | background writer| 23630 | | checkpointer| 23632 | | walwriter (11 rows)-- 對應進程信息 [root@dmpg1 12661]# ps -ef |grep 60011 postgres 60011 23627 0 17:07 ? 00:00:00 postgres: postgres zoo 192.168.131.1(65478) idle root 64115 42950 0 18:24 pts/2 00:00:00 grep --color=auto 60011

-- 3) 用pg_terminate_backend函數殺掉會話，能殺掉

postgres=# SELECT datname,pid,state,backend_type FROM pg_stat_activity;datname | pid | state | backend_type -----------+-------+--------+------------------------------| 23635 | | logical replication launcher| 23633 | | autovacuum launcherpostgres | 63810 | active | client backendpostgres | 60710 | idle | client backendpostgres | 59702 | idle | client backendzoo | 59736 | idle | client backendsample_db | 59772 | idle | client backendzoo | 60011 | idle | client backend| 23631 | | background writer| 23630 | | checkpointer| 23632 | | walwriter (11 rows)postgres=# SELECT pg_terminate_backend(60011);pg_terminate_backend ----------------------t (1 row)postgres=# SELECT datname,pid,state,backend_type FROM pg_stat_activity;datname | pid | state | backend_type -----------+-------+--------+------------------------------| 23635 | | logical replication launcher| 23633 | | autovacuum launcherpostgres | 63810 | active | client backendpostgres | 60710 | idle | client backendpostgres | 59702 | idle | client backendzoo | 59736 | idle | client backendsample_db | 59772 | idle | client backend| 23631 | | background writer| 23630 | | checkpointer| 23632 | | walwriter (10 rows)

----生成殺會話的語句

postgres=# SELECT 'SELECT pg_terminate_backend(' || PID || ');' KILL_PID, DATID, DATNAME, PID, USESYSID, USENAME, APPLICATION_NAME, CLIENT_ADDR, CLIENT_PORT, STATE, QUERY FROM PG_STAT_ACTIVITY WHERE state='idle' limit 1;kill_pid | datid | datname | pid | usesysid | usename | application_name | client_addr | client_port | state | query -------------------------------------+-------+---------+-------+----------+----------+--------------------------+---------------+-------------+-------+----------------------------------------------------------------------------------------------------------------------- ------------------------------------SELECT pg_terminate_backend(72715); | 16387 | zoo | 72715 | 10 | postgres | pgAdmin 4 - CONN:4188715 | 192.168.131.1 | 49588 | idle | SELECT oid, pg_catalog.format_type(oid, NULL) AS typname FROM pg_catalog.pg_type WHERE oid IN (25, 26, 19, 23, 26, 19,25, 869, 23, 25, 25) ORDER BY oid; (1 row)

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