Re: Questions: transaction log and commit

kpoon_at_news.hk.super.net (Kin-Lin POON) wrote:

>Hi all Oracle gurus,
>
>I have a question about the transaction log which have
>puzzled me for a long time. What I know about the
>relationship between the transaction log and the commit is
>that, when a user do a commit, the transaction log buffer in
>the SGA will be immediately flushed into the disc so that
>if the DB crash, we can still recover the transaction made by
>following the transaction log.
>
>However, when the Oracle DB engine issue a OS call asking
>for a write service, the OS may pend this call and store
>the data in the cache, waiting for a batch write. So
>what may happen is that when a user do a commit, the log
>in the SGA which is supposed to be written to the disc
>immediately, is still in the OS cache buffer, awaiting
>to be flushed to the disc. If the machine shutdown at
>this point, then the log will not be written to the disc
>and we cannot recover the data after a commit.
>
>Is there something wrong with the above reasoning? Can
>anyone tell me if this will be a potential danger to data
>loss?
>
>Thx a lot.
>KP.
>--
>Poon Kin-Lin. kpoon_at_hk.super.net http://www.hk.super.net/~kpoon
> 852.252.56.531

Oracle forces a write through any OS buffer cache when the redo log buffer is flushed.

Steve Received on Thu May 30 1996 - 00:00:00 CEST