Oracle Scratchpad

April 7, 2022

Parallel Inactivity

Filed under: Oracle,Parallel Execution,Performance,Troubleshooting — Jonathan Lewis @ 5:08 pm BST Apr 7,2022

This is a simple script that I wrote more than 20 years ago (for 8.1.7.4 apparently) to get the session wait event figures from parallel query slaves as they were running. I’m posting it now because there’s a question on the Oracle Database Forum where it would be useful as a way for checking for performance problems in a long-running CTAS.

Oracle gives us the view v$px_session to link together the query co-ordinator with the parallel query slaves, and it gives us v$px_sesstat to report the linked session activity stats, but it doesn’t gives us a view to link together the session events for the multiple sessions, so this query simply joins v$px_session to v$session_events to produce that result:

rem
rem     Script:         px_waits.sql
rem     Author:         Jonathan Lewis
rem     Dated:          Mar 2001
rem     Purpose:        Report events for PX execution
rem
rem     Last tested:
rem             19.3.0.0
rem
rem     Notes:
rem     Note that the co-ordinator can be on a different instance
rem     in parallel server systems.  To cater for an oddity of the
rem     qcinst report, we need the current instance number in case
rem     the QC is on the current machine.
rem
rem     If the co-ordinator is present, then it appears last on the list
rem     for a server group.
rem

column instance_number new_value m_inst
select instance_number from v$instance;

set linesize 120
set pagesize 60
set trimspool on
set tab off
set verify off

spool px_waits

break -
        on qcsid skip 1 -
        on server_group -
        on degree -
        on server_set -
        on sid -
        on server# skip 1

column event format a32

column  qcsid           format a6       heading 'Coord'
column  server_group    format 999      heading 'Grp'
column  degree          format a5       heading 'Deg'   noprint
column  server_set      format 999      heading 'Set'   noprint
column  server#         format 999      heading 'Sno'
column  sid             format 9999     heading 'SID'
column  name            format a32      heading 'Statistic'
column  value           format 99,999,999       heading 'value'

select
        ss.qcsid || '/' || nvl(ss.qcinst_id,&m_inst)            qcsid,
        ss.server_group,
        decode(degree,
                null,null,
                ss.degree || '/' || ss.req_degree
        )       degree,
        ss.server_set,
        ss.server#,
        ss.sid,
        se.event,
        se.total_waits,
        se.time_waited
from
        v$px_session            ss,
        v$session_event         se
where
        se.sid = ss.sid
order by
        ss.qcsid,
        ss.server_group,
        ss.server_set,
        ss.server#,
        se.event
;

clear columns
clear breaks
set verify on

spool off

See also: Parallel Activity for the session activity stats report.

2 Comments »

  1. […] also: Parallel Inactivity for a simple script reporting wait […]

    Pingback by Parallel Activity | Oracle Scratchpad — April 7, 2022 @ 5:09 pm BST Apr 7,2022 | Reply

  2. […] showing all the hints, their inverses, and the level(s) for which they’re relevant. Parallel Wait Events: simple listing for the wait events for all the processes involved in a parallel query. Parallel […]

    Pingback by Simple scripts | Oracle Scratchpad — April 7, 2022 @ 5:20 pm BST Apr 7,2022 | Reply


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