Monitoring Oracle Parallel Query with STATSPACK

In addition to monitoring parallel execution for individual queries, you can also monitor parallel query activity for your whole database. Using STATSPACK, you can query the stats$sysstat table to extract the number of parallelized queries that have been run during each time period between your STATSPACK snapshots. Here is the script that I use to monitor parallel queries:


rpt_parallel.sql
set pages 9999;

column nbr_pq format 999,999,999
column mydate heading 'yr. mo dy Hr.'

select
to_char(snap_time,'yyyy-mm-dd HH24') mydate,
new.value nbr_pq
from
perfstat.stats$sysstat old,
perfstat.stats$sysstat new,
perfstat.stats$snapshot sn
where
new.name = old.name
and
new.name = 'queries parallelized'
and
new.snap_id = sn.snap_id
and
old.snap_id = sn.snap_id-1
and
new.value > 1
order by
to_char(snap_time,'yyyy-mm-dd HH24')
;



Here is a sample of the output. This will quickly show the DBA the time periods when parallel full-table scans are being invoked:



SQL> @rpt_parallel

yr. mo dy hr. nbr_pq
------------- -------------
2001-03-12 20 3,521
2001-03-12 21 2,082
2001-03-12 22 2,832
2001-03-13 20 5,152
2001-03-13 21 1,835
2001-03-13 22 2,623
2001-03-14 20 4,274
2001-03-14 21 1,429
2001-03-14 22 2,313



In this example, we see that there appears to be a period each day between 8:00 p.m. and 10:00 p.m. when tasks are executing parallel queries against tables.

In practice, you may want to run the STATSPACK report to identify periods of high parallel query activity and then go to the stats$sql_summary table to examine and tune the individual parallel queries. Of course, you can also examine parallel query summaries since database start-up time by using the v$pq_sysstat view.



For additional details see the Oracle Press Book “Oracle High Performance Tuning with STATSPACK“.