目录

pg_advisory_lock_shared()

用于获取共享会话级咨询锁的函数

pg_advisory_lock_shared() 是一个用于获取共享会话级 咨询锁 的系统函数。

pg_advisory_lock_shared() 添加于 PostgreSQL 8.2。

用法

pg_advisory_lock_shared ( key bigint ) → void
pg_advisory_lock_shared ( key1 integer, key2 integer ) → void

pg_advisory_lock_shared() 将会无限期等待以获取指定的锁。如果想在获取锁或者在锁不可用时立即返回，请使用 pg_try_advisory_lock_shared()。

如果另一个会话持有共享会话级的咨询锁，则无法获取排他的会话级咨询锁。

变更历史

示例

pg_advisory_lock_shared() 的基本用法示例

postgres=# SELECT pg_advisory_lock_shared(123);
 pg_advisory_lock_shared
-------------------------

(1 row)

此时将在 pg_locks 中有一个对应的条目

postgres=# SELECT locktype, database, objid, objsubid, mode, pid, granted, fastpath
             FROM pg_locks
            WHERE locktype = 'advisory';
 locktype | database | objid | objsubid |   mode    |   pid   | granted | fastpath
----------+----------+-------+----------+-----------+---------+---------+----------
 advisory |        5 |   123 |        1 | ShareLock | 3820555 | t       | f
(1 row)

可以从不同的会话获取另一个共享咨询锁

postgres=# SELECT pg_backend_pid();
 pg_backend_pid 
----------------
        3823496
(1 row)

postgres=# SELECT pg_advisory_lock_shared(123);
 pg_advisory_lock_shared 
-------------------------
 
(1 row)

postgres=# SELECT locktype, database, objid, objsubid, mode, pid, granted, fastpath
             FROM pg_locks
            WHERE locktype = 'advisory';
 locktype | database | objid | objsubid |   mode    |   pid   | granted | fastpath 
----------+----------+-------+----------+-----------+---------+---------+----------
 advisory |        5 |   123 |        1 | ShareLock | 3823496 | t       | f
 advisory |        5 |   123 |        1 | ShareLock | 3820555 | t       | f
(2 rows)

如果持有锁的会话结束（在此示例中为之前的会话），则锁将被释放（即不再存在）

postgres=# \c - foo
You are now connected to database "postgres" as user "foo".

postgres=> SELECT locktype, database, objid, objsubid, mode, pid, granted, fastpath
             FROM pg_locks
            WHERE locktype = 'advisory';
 locktype | database | objid | objsubid |   mode    |   pid   | granted | fastpath 
----------+----------+-------+----------+-----------+---------+---------+----------
 advisory |        5 |   123 |        1 | ShareLock | 3820555 | t       | f
(1 row)

分类

锁定, 系统函数

另请参阅

pg_try_advisory_lock_shared(), pg_advisory_unlock_shared(), pg_advisory_unlock_all(), pg_advisory_lock(), 咨询锁

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