psotgres 鎖
1、因爲事物產生的鎖
操作：
session A
postgres=# drop table test2;
DROP TABLE
postgres=# create table test2(id int, info text);
CREATE TABLE
postgres=# insert into test2 values (1,'test');
INSERT 0 1
postgres=# begin;
BEGIN
postgres=# update test2 set info='a' where id=1;
UPDATE 1
session B
postgres=# update test2 set info='b' ;
（此時會等待）
事前配置：
配置以下內容日誌中將會記錄鎖等待的情況
log_lock_waits = on
deadlock_timeout = 1s
解決方法：
1：通過日誌
2016-12-23 14:35:35 CST [5847-9] postgres@postgres LOG: process 5847 still waiting for ShareLock on transaction 1162758 after 1007.019 ms
2016-12-23 14:35:35 CST [5847-10] postgres@postgres DETAIL: Process holding the lock: 5840. Wait queue: 5847.
2016-12-23 14:35:35 CST [5847-11] postgres@postgres CONTEXT: while updating tuple (0,3) in relation "test2"
2016-12-23 14:35:35 CST [5847-12] postgres@postgres STATEMENT: update test2 set info='b' ;
2：通過命令
session C
postgres=# select b.* from pg_class a,pg_locks b where a.oid=b.relation and a.relname='test2';
relation | 12415 | 16438 | | | | | | | | 3/14 | 5847 | RowExclusiveLock | t | t
relation | 12415 | 16438 | | | | | | | | 2/18 | 5840 | RowExclusiveLock | t | t
tuple | 12415 | 16438 | 0 | 3 | | | | | | 3/14 | 5847 | ExclusiveLock | t | f
看到鎖類型爲tuple，數據庫oid爲12415 被鎖定目標爲：16438
kill 掉對應的的進程即可
備註：
通過oid查看數據庫名
select oid,datname from pg_database where oid=12415;
12415 | postgres
通過oid查看錶名
select oid,relname from pg_class where oid=16438;
16438 | test2
查看某個pid正在執行的命令
SELECT
procpid,
start,
now() - start AS lap,
current_query
FROM
(SELECT
backendid,
pg_stat_get_backend_pid(S.backendid) AS procpid,
pg_stat_get_backend_activity_start(S.backendid) AS start,
pg_stat_get_backend_activity(S.backendid) AS current_query
FROM
(SELECT pg_stat_get_backend_idset() AS backendid) AS S
) AS S
WHERE
current_query <> '<IDLE>' and procpid=5847
ORDER BY
lap DESC;
kill 掉對應的進程即可