查看表锁信息，是DBA常用的脚本之一。
实验环境：
CentOS 7
PG 10.4
先通过A窗口执行
mytest=# begin;
BEGIN
mytest=# update t1 set col1 = 'a' where id =1 ;
UPDATE 1
mytest=#
打开B窗口执行
mytest=# begin;
BEGIN
mytest=# update t1 set col1 = 'b' where id =2;
UPDATE 1
mytest=# update t1 set col1 = 'b' where id =1;
等待了
说明只锁住了行，对于更新其他行没有影响。
再打开一个窗口查看信息
SELECT
a.datname,
locktype,
virtualtransaction,
transactionid,
nspname,
relname,
mode,
granted,
cast(date_trunc('second',query_start) AS timestamp) AS query_start
FROM
pg_locks
LEFT OUTER JOIN pg_class ON (pg_locks.relation = pg_class.oid)
LEFT OUTER JOIN pg_namespace ON (pg_namespace.oid = pg_class.relnamespace),
pg_stat_activity a
WHERE NOT pg_locks.pid = pg_backend_pid()
AND pg_locks.pid=a.pid;
datname | locktype | virtualtransaction | transactionid | nspname | relname | mode | granted | query_start
---------+---------------+--------------------+---------------+---------+---------+------------------+---------+---------------------
mytest | relation | 7/332 | | public | t1 | RowExclusiveLock | t | 2018-06-28 06:29:58
mytest | virtualxid | 7/332 | | | | ExclusiveLock | t | 2018-06-28 06:29:58
mytest | relation | 6/42 | | public | t1 | RowExclusiveLock | t | 2018-06-28 06:29:35
mytest | virtualxid | 6/42 | | | | ExclusiveLock | t | 2018-06-28 06:29:35
mytest | transactionid | 7/332 | 712 | | | ExclusiveLock | t | 2018-06-28 06:29:58
mytest | transactionid | 6/42 | 711 | | | ExclusiveLock | t | 2018-06-28 06:29:35
mytest | transactionid | 7/332 | 711 | | | ShareLock | f | 2018-06-28 06:29:58
mytest | tuple | 7/332 | | public | t1 | ExclusiveLock | t | 2018-06-28 06:29:58
(8 rows)