Re: _wait_for_sync , dirty buffer flushing and direct reads in parallel query

_wait_for_sync basically meant that a session is waiting for the sync of the redo by the lgwr. Normally the redo log writer writes to disk and then notifies the session that the transaction is completed. By setting this to false, you no longer wait for the redo to go to disk.

That has no impact on your situation.

Anjo.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, November 19, 2003 11:20 PM query

> Hi!
>
> I've sometimes used setting _wait_for_sync=false during Apps upgrade
> projects, to upgrade performance. (As long as your database doesn't crash
> during the parameter is set to false, no problems should occur).
>
> I just started wondering, what would be the case if a parallel query
starts
> during someone is modifying data...
>
> As I understand, when doing parallel query:
> 1) the dirty blocks which are supposed to be read by PQ in direct mode,
are
> flushed to disk
> 2) PQ reads the blocks in direct mode
>
> But when _wait_for_sync is set, the writes get acknowledged immediately
(or
> acknowledgement is not waited for). Could this result in the unlikely
> situation, that PQ issues the flush command to dirty buffers and starts to
> read them, but actually reads the old images of the blocks, since it
thinks
> the write has already occurred?
>
> (actually, this doesn't touch only PQ, it's possible to have direct reads
to
> PGA in serial mode too...)
>
> Tanel.
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Tanel Poder
> INET: tanel.poder.003_at_mail.ee
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Anjo Kolk
  INET: anjo_at_oraperf.com

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