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: [EMAIL PROTECTED]
>Reply-To: [EMAIL PROTECTED]
>To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
>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" <[EMAIL PROTECTED]>
>Sent by: [EMAIL PROTECTED]
>06/08/01 07:40 AM
>Please respond to ORACLE-L
>
>
> To: Multiple recipients of list ORACLE-L
><[EMAIL PROTECTED]>
> 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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