咨询锁函数用于管理咨询锁（Advisory Lock）。

• pg_advisory_lock(key bigint)

  描述：获取会话级别的排他咨询锁。

  返回值类型：void

  备注：pg_advisory_lock锁定应用程序定义的资源，该资源可以用一个64位或两个不重叠的32位键值标识。如果已经有另外的会话锁定了该资源，则该函数将阻塞到该资源可用为止。这个锁是排他的。多个锁定请求将会被压入栈中，因此，如果同一个资源被锁定了三次，它必须被解锁三次以将资源释放给其他会话使用。

• pg_advisory_lock(key1 int, key2 int)

  描述：获取会话级别的排他咨询锁。

  返回值类型：void

  备注：只允许sysadmin对键值对(65535, 65535)加会话级别的排他咨询锁，普通用户无权限。

• pg_advisory_lock(lock_id int4, lock_id int4, datebase_name Name)

  描述：通过传入锁ID和数据库名字，获取指定数据库的排他咨询锁。

  返回值类型：void

• pg_advisory_lock_shared(key bigint)

  描述：获取会话级别的共享咨询锁。

  返回值类型：void

• pg_advisory_lock_shared(key1 int, key2 int)

  描述：获取会话级别的共享咨询锁。

  返回值类型：void

  备注：pg_advisory_lock_shared类似于pg_advisory_lock，不同之处仅在于共享锁会话可以和其他请求共享锁的会话共享资源，但排他锁除外。

• pg_advisory_unlock(key bigint)

  描述：释放会话级别的排他咨询锁。

  返回值类型：Boolean

• pg_advisory_unlock(key1 int, key2 int)

  描述：释放会话级别的排他咨询锁。

  返回值类型：Boolean

  备注：pg_advisory_unlock释放先前取得的排他咨询锁。如果释放成功则返回true。如果实际上并未持有指定的锁，将返回false并在服务器中产生一条SQL警告信息。

• pg_advisory_unlock(lock_id int4, lock_id int4, datebase_name Name)

  描述：通过传入锁ID和数据库名字，释放指定数据库上的排他咨询锁。

  返回值类型：Boolean

  备注：如果释放成功则返回true；如果未持有锁，则返回false。

• pg_advisory_unlock_shared(key bigint)

  描述：释放会话级别的共享咨询锁。

  返回值类型：Boolean

• pg_advisory_unlock_shared(key1 int, key2 int)

  描述：释放会话级别的共享咨询锁。

  返回值类型：Boolean

  备注：pg_advisory_unlock_shared类似于pg_advisory_unlock，不同之处在于该函数释放的是共享咨询锁。

• pg_advisory_unlock_all()

  描述：释放当前会话持有的所有咨询锁。

  返回值类型：void

  备注：pg_advisory_unlock_all将会释放当前会话持有的所有咨询锁，该函数在会话结束的时候被隐含调用，即使客户端异常地断开连接也是一样。

• pg_advisory_xact_lock(key bigint)

  描述：获取事务级别的排他咨询锁。

  返回值类型：void

• pg_advisory_xact_lock(key1 int, key2 int)

  描述：获取事务级别的排他咨询锁。

  返回值类型：void

  备注：pg_advisory_xact_lock类似于pg_advisory_lock，不同之处在于锁是自动在当前事务结束时释放，而且不能被显式的释放。只允许sysadmin对键值对(65535, 65535)加事务级别的排他咨询锁，普通用户无权限。

• pg_advisory_xact_lock_shared(key bigint)

  描述：获取事务级别的共享咨询锁。

  返回值类型：void

• pg_advisory_xact_lock_shared(key1 int, key2 int)

  描述：获取事务级别的共享咨询锁。

  返回值类型：void

  备注：pg_advisory_xact_lock_shared类似于pg_advisory_lock_shared，不同之处在于锁是在当前事务结束时自动释放，而且不能被显式的释放。

• pg_try_advisory_lock(key bigint)

  描述：尝试获取会话级排他咨询锁。

  返回值类型：Boolean

  备注：pg_try_advisory_lock类似于pg_advisory_lock，不同之处在于该函数不会阻塞以等待资源的释放。它要么立即获得锁并返回true，要么返回false表示目前不能锁定。

• pg_try_advisory_lock(key1 int, key2 int)

  描述：尝试获取会话级排他咨询锁。

  返回值类型：Boolean

  备注：只允许sysadmin对键值对(65535, 65535)加会话级别的排他咨询锁，普通用户无权限。

• pg_try_advisory_lock_shared(key bigint)

  描述：尝试获取会话级共享咨询锁。

  返回值类型：Boolean

• pg_try_advisory_lock_shared(key1 int, key2 int)

  描述：尝试获取会话级共享咨询锁。

  返回值类型：Boolean

  备注：pg_try_advisory_lock_shared类似于pg_try_advisory_lock，不同之处在于该函数尝试获得共享锁而不是排他锁。

• pg_try_advisory_xact_lock(key bigint)

  描述：尝试获取事务级别的排他咨询锁。

  返回值类型：Boolean

• pg_try_advisory_xact_lock(key1 int, key2 int)

  描述：尝试获取事务级别的排他咨询锁。

  返回值类型：Boolean

  备注：pg_try_advisory_xact_lock类似于pg_try_advisory_lock，不同之处在于如果得到锁，在当前事务的结束时自动释放，而且不能被显式的释放。只允许sysadmin对键值对(65535, 65535)加事务级别的排他咨询锁，普通用户无权限。

• pg_try_advisory_xact_lock_shared(key bigint)

  描述：尝试获取事务级别的共享咨询锁。

  返回值类型：Boolean

• pg_try_advisory_xact_lock_shared(key1 int, key2 int)

  描述：尝试获取事务级别的共享咨询锁。

  返回值类型：Boolean

  备注：pg_try_advisory_xact_lock_shared类似于pg_try_advisory_lock_shared，不同之处在于如果得到锁，在当前事务结束时自动释放，而且不能被显式的释放。

• lock_cluster_ddl()

  描述：尝试对数据库内所有存活的数据库主节点获取会话级别的排他咨询锁。

  返回值类型：Boolean

  备注：只允许sysadmin调用，普通用户无权限。

• unlock_cluster_ddl()

  描述：尝试对数据库主节点会话级别的排他咨询锁。

  返回值类型：Boolean

  会话级别咨询锁示例：

  gaussdb=# select pg_advisory_lock(1); --依次获取3个会话级别的咨询锁
   pg_advisory_lock 
  ------------------
  (1 row)
  
  gaussdb=# select pg_advisory_lock(1,2);
   pg_advisory_lock 
  ------------------
  (1 row)
  gaussdb=# select pg_advisory_lock(2,2,'postgres');
   pg_advisory_lock 
  ------------------
  (1 row)
  
  gaussdb=# select * from pg_locks;  --查询pg_locks表，看到新增了3个advisory类型的锁
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27611            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27611    |               |         |       |          | 4/27611            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6bd
  b:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16219   |               |         |       |          | 19/16219           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:3f
  5b:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/97293   |               |         |       |          | 17/97293           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:17
  c0d:0:0:0:7  | 0:0#0
   advisory   |    12850 |          |      |       |        |            |               |       0 |     1 |        1 | 4/27611            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | f        | 3232:
  0:1:1:0:b    | 0:0#0
   advisory   |    12850 |          |      |       |        |            |               |       1 |     2 |        2 | 4/27611            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | f        | 3232:
  1:2:2:0:b    | 0:0#0
   advisory   |    12850 |          |      |       |        |            |               |       2 |     2 |        2 | 4/27611            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | f        | 3232:
  2:2:2:0:b    | 0:0#0
  (7 rows)
  
  gaussdb=# select pg_advisory_unlock(1);  --依次释放3个会话级别的咨询锁
   pg_advisory_unlock 
  --------------------
   t
  (1 row)
  
  gaussdb=# select pg_advisory_unlock(1,2);
   pg_advisory_unlock 
  --------------------
   t
  (1 row)
  
  gaussdb=# select pg_advisory_unlock(2,2,'postgres');
   pg_advisory_unlock 
  --------------------
   t
  (1 row)
  
  gaussdb=# select * from pg_locks;  --查询pg_locks表，看到3个advisory类型的锁已被释放
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27618            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27618    |               |         |       |          | 4/27618            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6be
  2:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16254   |               |         |       |          | 19/16254           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:3f
  7e:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/97506   |               |         |       |          | 17/97506           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:17
  ce2:0:0:0:7  | 0:0#0
  (4 rows)
  
  gaussdb=# select pg_advisory_lock(1); --再次获取会话级别的咨询锁
   pg_advisory_lock 
  ------------------
  
  (1 row)
  
  gaussdb=# select pg_advisory_unlock_all();  --释放所有会话级别的咨询锁
   pg_advisory_unlock_all 
  ------------------------
  
  (1 row)
  
  gaussdb=# select * from pg_locks;  --查询pg_locks表，看到advisory类型的锁已被释放
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27629            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27629    |               |         |       |          | 4/27629            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6be
  d:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16369   |               |         |       |          | 19/16369           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:3f
  f1:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/98194   |               |         |       |          | 17/98194           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:17
  f92:0:0:0:7  | 0:0#0
  (4 rows)

  事务级别咨询锁示例：

  gaussdb=# select pg_advisory_xact_lock_shared(1); --获取事务级别的共享咨询锁
   pg_advisory_xact_lock_shared 
  ------------------------------
  (1 row)
  
  gaussdb=# select * from pg_locks; --因单条语句视为一个事务，因此咨询锁已随事务提交自动释放。查询pg_locks表，看不到事务级咨询锁
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27631            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27631    |               |         |       |          | 4/27631            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6be
  f:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16396   |               |         |       |          | 19/16396           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:40
  0c:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/98359   |               |         |       |          | 17/98359           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:18
  037:0:0:0:7  | 0:0#0
  (4 rows)
  
  gaussdb=# start transaction;  --显式开启事务块
  START TRANSACTION
  gaussdb=# select pg_advisory_xact_lock_shared(1);  --获取事务级别的共享咨询锁
   pg_advisory_xact_lock_shared 
  ------------------------------
  
  (1 row)
  
  gaussdb=# select * from pg_locks;  --查询pg_locks表，新增了一个advisory类型锁
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27632            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27632    |               |         |       |          | 4/27632            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6bf
  0:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16399   |               |         |       |          | 19/16399           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:40
  0f:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/98377   |               |         |       |          | 17/98377           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:18
  049:0:0:0:7  | 0:0#0
   advisory   |    12850 |          |      |       |        |            |               |       0 |     1 |        1 | 4/27632            | 140245958915840 | 140245958915840 | ShareLock       | t       | f        | 3232:
  0:1:1:0:b    | 0:0#0
  (5 rows)
  
  gaussdb=# commit;  --提交事务块
  COMMIT
  gaussdb=# select * from pg_locks;  --查询pg_locks表，事务级别advisory类型锁已自动释放
    locktype  | database | relation | page | tuple | bucket | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction |       pid       |    sessionid    |      mode       | granted | fastpath |      
  locktag      | global_sessionid 
  ------------+----------+----------+------+-------+--------+------------+---------------+---------+-------+----------+--------------------+-----------------+-----------------+-----------------+---------+----------+------
  -------------+------------------
   relation   |    12850 |    10652 |      |       |        |            |               |         |       |          | 4/27633            | 140245958915840 | 140245958915840 | AccessShareLock | t       | t        | 3232:
  299c:0:0:0:0 | 0:0#0
   virtualxid |          |          |      |       |        | 4/27633    |               |         |       |          | 4/27633            | 140245958915840 | 140245958915840 | ExclusiveLock   | t       | t        | 4:6bf
  1:0:0:0:7    | 0:0#0
   virtualxid |          |          |      |       |        | 19/16401   |               |         |       |          | 19/16401           | 140246771033856 | 140246771033856 | ExclusiveLock   | t       | t        | 13:40
  11:0:0:0:7   | 0:0#0
   virtualxid |          |          |      |       |        | 17/98385   |               |         |       |          | 17/98385           | 140246750590720 | 140246750590720 | ExclusiveLock   | t       | t        | 11:18
  051:0:0:0:7  | 0:0#0
  (4 rows)

  尝试获取咨询锁示例：

  gaussdb=# select pg_try_advisory_lock_shared(1); --在没有其他连接加咨询锁时，尝试获取对象1的共享咨询锁成功
   pg_try_advisory_lock_shared 
  -----------------------------
   t
  (1 row)
  
  gaussdb=# select pg_advisory_unlock_all();  --释放这个咨询锁
   pg_advisory_unlock_all 
  ------------------------
  
  (1 row)
  
  gaussdb=# select pg_advisory_lock(1); --获取对象1的排他咨询锁
   pg_advisory_lock 
  ------------------
  
  (1 row)
  
  --保持这个连接不断开，新启动一个连接
  gaussdb=# select pg_try_advisory_lock_shared(1); --因已有连接持有排他锁，所以新连接中尝试获取对象1的共享咨询锁失败
   pg_try_advisory_lock_shared 
  -----------------------------
   f
  (1 row)