我们在使用 PostgreSQL 的时候经常会遇到有关锁的信息。那么如何判断是否有死锁或者锁等待呢？
WITH lock_pid AS (
SELECT DISTINCT pid
FROM pg_locks
WHERE pid <> pg_backend_pid() )

SELECT psa.*
FROM pg_stat_activity psa
INNER JOIN lock_pid lp ON psa.pid = lp.pid;

SELECT l.locktype,
       l.database,
       l.relation,
       l.page,
       l.tuple,
       l.virtualxid,
       l.transactionid,
       l.classid,
       l.objid,
       l.objsubid,
       l.pid AS blocking_pid,
       l.mode AS lock_mode,
       l.granted,
       s1.datname AS database_name,
       s1.usename AS blocking_user,
       s1.query AS blocking_query
FROM pg_locks l
INNER JOIN pg_stat_activity s1 ON l.pid = s1.pid
INNER JOIN pg_locks l2 ON l.database = l2.database
    AND l.relation = l2.relation
    AND l.page = l2.page
    AND l.tuple = l2.tuple
    AND l.pid <> l2.pid
INNER JOIN pg_stat_activity s2 ON l2.pid = s2.pid;

        l.locktype, --可锁的对象的类型
        l.database, --锁目标存在的数据库的 OID
        l.relation, --作为锁目标的关系的 OID
        l.page, --作为锁目标的页在关系中的页号
        l.tuple, --作为锁目标的元组在页中的元组号
        l.virtualxid, --作为锁目标的事务虚拟 ID
        l.transactionid, --作为锁目标的事务 ID
        l.classid, --包含锁目标的系统目录的 OID
        l.objid, --锁目标在它的系统目录中的OID
        l.objsubid, --锁的目标列号
        l.pid AS blocking_pid, --保持这个锁或者正在等待这个锁的服务器进程的 PID
        l.mode AS lock_mode, --此进程已持有或者希望持有的锁模式
        l.granted --锁已授予则为真否则为假