Parallel select, excessive IO and parallel_execution_message_siz

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Date: Mon, 23 Apr 2012 17:23:32 +0300
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Did anyone experience this phenomena of parallel select:

select /*+parallel ( 2) */ went reading one segment like crazy - disk reads many times over the segment(table) size. The finding was supported by v$sql, v$sesstat and AWR reports.

The plan was a hash join of two tables plus a filter (select from 2 records table)

After the parallel_execution_message_size was bumped to maximum (64k) and oracle server bounced the select completed within expected time and IO limits.

Can parallel_execution_message_size affect IO (and time) of parallel select so drastically ?

Thank you in advance, Laimis N

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-- Received on Mon Apr 23 2012 - 09:23:32 CDT

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