pg_stat_activity - View in PostgreSQL

 

Fields of the pg_stat_activity view

View connection information

You can execute the following SQL statement to view the connected users and their clients:

SELECT datname,usename,client_addr,client_port FROM pg_stat_activity ;

datname  |  usename  |  client_addr   | client_port
---------+----------+---------------+-------------
postgres | joe       |  xx.xx.xx.xx   |       60621
postgres | gpmon     |  xx.xx.xx.xx   |       60312
(9 rows)

Query the SQL execution information

You can execute the following SQL statements to view current queries executed by users who connect to the database:

AnalyticDB for PostgreSQL V6.0:

SELECT datname,usename,query FROM pg_stat_activity ;

 datname  | usename  |                        query
----------+---------+--------------------------------------------------------------
 postgres | postgres | SELECT datname,usename,query FROM pg_stat_activity ;
 postgres | joe      | 
(2 rows)

AnalyticDB for PostgreSQL V4.3:

SELECT datname,usename,current_query FROM pg_stat_activity ;

 datname  | usename  |                        current_query
----------+---------+--------------------------------------------------------------
 postgres | postgres | SELECT datname,usename,current_query FROM pg_stat_activity ;
 postgres | joe      | <IDLE>
(2 rows)

You can execute the following SQL statements to view active queries:

AnalyticDB for PostgreSQL V6.0:

SELECT datname,usename,query
   FROM pg_stat_activity
   WHERE state != 'idle' ;

AnalyticDB for PostgreSQL V4.3:

SELECT datname,usename,current_query
   FROM pg_stat_activity
   WHERE current_query != '<IDLE>' ;

View long-running queries

You can execute the following SQL statements to view long-running queries:

AnalyticDB for PostgreSQL V6.0:

select current_timestamp - query_start as runtime, datname, usename, query
    from pg_stat_activity
    where state != 'idle'
    order by 1 desc;

AnalyticDB for PostgreSQL V4.3:

select current_timestamp - query_start as runtime, datname, usename, current_query
    from pg_stat_activity
    where current_query != '<IDLE>'
    order by 1 desc;

Sample query results:

runtime         |    datname     | usename  |                                current_query
----------------+---------------+---------+------------------------------------------------------------------------------
 00:00:34.248426 | tpch_1000x_col | postgres | select
                                             :         l_returnflag,
                                             :         l_linestatus,
                                             :         sum(l_quantity) as sum_qty,
                                             :         sum(l_extendedprice) as sum_base_price,
                                             :         sum(l_extendedprice * (1 - l_discount)) as sum_disc_price,
                                             :         sum(l_extendedprice * (1 - l_discount) * (1 + l_tax)) as sum_charge,
                                             :         avg(l_quantity) as avg_qty,
                                             :         avg(l_extendedprice) as avg_price,
                                             :         avg(l_discount) as avg_disc,
                                             :         count(*) as count_order
                                             : from
                                             :         public.lineitem
                                             : where
                                             :         l_shipdate <= date '1998-12-01' - interval '93' day
                                             : group by
                                             :         l_returnflag,
                                             :         l_linestatus
                                             : order by
                                             :         l_returnflag,
                                             :         l_linestatus;
 00:00:00        | postgres       | postgres | select
                                             :        current_timestamp - query_start as runtime,
                                             :        datname,
                                             :        usename,
                                             :        current_query
                                             :     from pg_stat_activity
                                             :     where current_query != '<IDLE>'
                                             :     order by 1 desc;
(2 rows)

The first returned query executes for a long time. The first query has been executing for 34 seconds and continues to execute.

Diagnose and troubleshoot abnormal SQL queries

If an SQL query has been executing for an extended period of time without returning a result, you must check whether the query has been blocked.

AnalyticDB for PostgreSQL V6.0:

SELECT datname,usename,query
   FROM pg_stat_activity
   WHERE waiting;

AnalyticDB for PostgreSQL V4.3:

SELECT datname,usename,current_query
   FROM pg_stat_activity
   WHERE waiting;

The preceding statements can return SQL queries that are blocked only due to lock waits. Queries that are blocked for other reasons are not returned. In most cases, SQL queries are blocked due to lock waits. However, in some other cases, SQL queries are blocked because they are waiting for I/O operations or timers. If the preceding statements have returned query results, specific SQL queries are blocked due to lock waits. You can execute the following statement to view details of these SQL queries:

SELECT
        w.query as waiting_query,
        w.pid as w_pid,
        w.usename as w_user,
        l.query as locking_query,
        l.pid as l_pid,
        l.usename as l_user,
        t.schemaname || '.' || t.relname as tablename
    from pg_stat_activity w
    join pg_locks l1 on w.pid = l1.pid and not l1.granted
    join pg_locks l2 on l1.relation = l2.relation and l2.granted
    join pg_stat_activity l on l2.pid = l.pid
    join pg_stat_user_tables t on l1.relation = t.relid
    where w.waiting;

The preceding statement can return the blocked SQL queries and their process IDs. You can review the details of the blocked SQL queries and then cancel or kill the queries to remove the blocks. You can execute the following statement to cancel an active query:

SELECT pg_cancel_backend(pid)

The pg_cancel_backend function can take effect only on active query sessions. The function does not affect idle sessions. In addition, canceling the query may take some time to clear sessions or roll back transactions. You can use pg_terminate_backend to clear idle sessions or terminate queries.

SELECT pg_terminate_backend(pid);

Connections initiated by the specified user are terminated. We recommend that you do not invoke the pg_terminate_backend function on processes identified by pid where active queries exist. To perform the operations mentioned in this topic, you must have superuser permissions.