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

From: Yong Huang <yong321_at_yahoo.com>
Date: Thu, 20 Nov 2003 07:10:00 -0800
Message-ID: <F001.005D7444.20031120071000@fatcity.com>

I think my understanding was wrong. _wait_for_sync actually only changes the behavior of foreground processes. When set to false, they don't wait for LGWR to write redo records to disk; instead they continue to do their work as if log file sync already finished. It *does not* change any behavior of LGWR, notification or not. Correct me if I'm wrong again.

I'm still interested in Tanel's benchmark, though. Only that is scientific.

Yong Huang

• Yong Huang <yong321_at_yahoo.com>, i.e. myself, wrote a few minutes ago:
  > Tanel,
  >
  > Did you observe better performance? By how much? Do please let us know!
  >
  > From what I read, _wait_for_sync when set to false means LGWR immediately
  > notifies user (foreground) processes that redo record writes are done (even
  > though they're not). When you say the parameter only affects LGWR, you need
  > to
  > clarify what you mean by "affect"; it changes the notification (posting)
  > behavior of LGWR therefore changes the behavior of waiting processes (*when*
  > they stop waiting). Just semantics.
  >
  > Yong Huang
  >
  > --- Tanel Poder <tanel.poder.003_at_mail.ee> wrote:
  > > Anjo,
  > >
  > > I also thought it affects only lgwr sync, but Jonathan Lewis once told that
  > > it affects any disk writes...
  > >
  > > If it affects only lgwr, then great, I can make Apps upgrades, which do
  > > really lots of DDLs and small transactions, quite much faster that way...
  > >
  > > Thank you,
  > > Tanel.
  > >
  > >
  > > > _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.
  

  ---

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Author: Yong Huang
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Received on Thu Nov 20 2003 - 09:10:00 CST