Well, some disk writes need to wait for the LGWR to flush the corresponding redo to disk. So now you can have a situation that the blocks that are dirty are on disk (without a commited transaction) but the redo is not yet. So if you crash in that period, you can't recover.
Anjo. ----- Original Message ----- To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> Sent: Thursday, November 20, 2003 2:59 PM parallel > 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. > > > > ----- Original Message ----- > > To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> > > Sent: Wednesday, November 19, 2003 11:20 PM > > query > > > > > > > Hi! > > > > > > I've sometimes used setting _wait_for_sync�lse 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: [EMAIL PROTECTED] > > > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > > San Diego, California -- Mailing list and web hosting > > services > > > > > --------------------------------------------------------------------- > > > To REMOVE yourself from this mailing list, send an E-Mail message > > > to: [EMAIL PROTECTED] (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). > > > > > > > -- > > Please see the official ORACLE-L FAQ: http://www.orafaq.net > > -- > > Author: Anjo Kolk > > INET: [EMAIL PROTECTED] > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > San Diego, California -- Mailing list and web hosting services > > --------------------------------------------------------------------- > > To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (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). > > > > > -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Anjo Kolk INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (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).
