Hash join ending up in huge wait events
523697Mar 6 2010 — edited Jan 12 2011Hi,
We are experiencing huge wait events ( direct path read temp , direct path write temp) on our Materialized View refresh in 10.2.0.4 version of oracle 10g in linux rhel5 environment while monitoring the refresh session from db console. While checking the explain plan of the mv query there is a huge hash_join (due to self join nature of the query) is shown. As advised in some dba forums, i have increased my pga_aggregate_target to a value of 4 gb from 1800 mb. The PGA_HIT % is raised to 60% from 58% ( just 2% improvement). But still my direct path read temp and direct path write temp wait event have not reduced and a huge temp space is taken for hash join.
Since we have some usage limit set by some hidden parameters for a each session on pga_aggregate_target, increase the size did not helped me much. The mv refresh is taking more than 5 hours ( sometimes it exceeds 5 hrs) to completes it refresh where as the same query in window (production) is completed less than two hours. Before a month, the refresh time in both environment was nearly close. But now it has changed and not able to figure it out.
STATISTICS have been collected regularly using dbms_gather_stats in both environment. Both mv refresh are scheduled to run using dbms_scheduler (Manual refresh). SGA_TARGET and other memory parameters are almost same.
Environment : Dataware house
O/s : RHEL 5
Oracle version : 10.2.0.4
Work_policy=auto
Is there any possibility to reduce this wait event and there by reducing the elapsed time? I am also interested to know changing the plan to use other sort will help? I don't know whether the details are sufficient to analyze this issue. If you need more details on this just let me know.
I really appreciate your help and thanks in advance to all.