Re: direct path read (temp) 31 blocks per event
Date: Fri, 14 Nov 2008 17:49:23 -0000
"HansP" <hans-peter.sloot_at_atosorigin.com> wrote in message
> Version 126.96.36.199
> Platform: Linux
> During a performance test I noticed the that 'direct path read temp'
> where done with 31 blocks and sometimes with 1 block per wait.
> The 'db file scattered read' 's where done with 128 blocks per wait
> (db_file_multiblock_read_count was not set explicitly)
> Does someone know why the strange number of 31 is chosen for the
> direct path reads (at least for temp).
> I think that normal direct path reads were als done with 31 blocks but
> I am not completely sure about that.
> BTW I looked in v$sesion_wait P3 is the block count.
> Any suggestions
> Regards Hans-Peter
It depends on the operation that had caused the direct path writes. If it was a hash join then the (dynamic) hash_io_multiblock_count would have been responsible for writing clusters of 31 blocks, so you would have to read clusters of the same size. Similarly if the sort_multiblock_read_count had dynamically adjusted itself to optimize the balance between size of reads and number of sort runs to merge, then 31 could just have appeared.
-- Regards Jonathan Lewis http://jonathanlewis.wordpress.com Author: Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.htmlReceived on Fri Nov 14 2008 - 11:49:23 CST