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Home -> Community -> Mailing Lists -> Oracle-L -> Re: parallel query performance
Riyaj,
Thanks for your reply. I have a follow up question. What happen when a
transaction is commited and the block has not been flushed out to disk yet?
If I have parallel query processes that need to read the commited blocks in
the buffer cache, then what happens. Since PQ processes do not read from
buffer cache, how do the processes access the updated blocks? The disk does
not have the updated information yet.
Thanks.
elain
>From: Riyaj_Shamsudeen_at_i2.com
>Reply-To: ORACLE-L_at_fatcity.com
>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>Subject: Re: parallel query performance
>Date: Fri, 08 Jun 2001 06:40:27 -0800
>
>Hi Elain
> Yes, that is true. SGA is useful if you want to cache the block,
>so that many sessions can avoid the disk reads. But, in case of Parallel
>Query architecture, mostly, only the parallel query slave is interested in
>the block. That's why slave process directly reads the blocks in to the
>PGA bypassing the Buffer cache. Of course, object level checkpoint occurs
>and there are some optimization in 8i versions. That is the reason, there
>is no point in increasing the buffer cache, if most of the work is done
>through parallel query slaves.
>
>But, the communication buffers between the slave processes are stored in
>the shared pool though.
>
>Thanks
>Riyaj "Re-yas" Shamsudeen
>Certified Oracle DBA
>i2 technologies www.i2.com
>
>
>
>
>"elain he" <elainhe_at_hotmail.com>
>Sent by: root_at_fatcity.com
>06/08/01 07:40 AM
>Please respond to ORACLE-L
>
>
> To: Multiple recipients of list ORACLE-L
><ORACLE-L_at_fatcity.com>
> cc:
> Subject: parallel query performance
>
>
>Hi,
>Is it true that when running parallel query, the parallel query slaves do
>not read from buffer cache even though the data resides in the buffer
>cache
>ie the slaves read directly from disk.
>
>Does not make sense to me. Can someone clarify that?
>
>Thanks.
>
>elain
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: elain he INET: elainhe_at_hotmail.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Fri Jun 08 2001 - 10:20:11 CDT
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