database - 锁定表行以防止数据修改

Question

CREATE TABLE t1 (
  id serial int,
  col text
);

insert into t1(col) values('old_value');

现在，我需要锁定该表以防止数据修改，而下面的 plsql block 正在运行

DO $$
  declare 
     res1 TEXT;
     res2 TEXT;
  BEGIN 
        --PERFORM pg_advisory_lock( )  
        select col from t1 where id = 1 into  res1;
        FOR i in 1..2000000000 LOOP
           -- this is just for waiting several second
        END LOOP;
        select col from t1 where id = 1 into  res2;
        RAISE NOTICE '% - %', res1, res2;
        --PERFORM pg_advisory_unlock( )  
  END;
  $$ LANGUAGE PLPGSQL

因此，当该 block 运行时，我运行其他查询:

update t1 SET col = 'new_value' where id = 1;

此查询会立即运行，并在运行 plsql block 未完成时更新行。

我需要相反，我需要在 plsql block 运行时更新未工作并等待。

我认为 pg_advisory_lock() 和 pg_advisory_unlock() 会有所帮助，但是如何使用它，我不明白，这些函数的关键参数是什么，我不明白。

而且也不确定这些功能是否有效。

如有任何帮助，我们将不胜感激。

Answer 1

您想要select col from t1 where id = 1 FOR UPDATE into res1;获得锁，所以整个 block 应该如下所示:

DO $$ declare res1 TEXT; res2 TEXT; BEGIN --PERFORM pg_advisory_lock( )<br/> select col from t1 where id = 1 into FOR UPDATE res1; FOR i in 1..2000000000 LOOP -- this is just for waiting several second END LOOP; select col from t1 where id = 1 into res2; RAISE NOTICE '% - %', res1, res2; --PERFORM pg_advisory_unlock( )<br/> END; $$ LANGUAGE PLPGSQL

参见http://www.postgresql.org/docs/9.4/static/explicit-locking.html