Re: Can a large log buffer cause data loss?

From: Thiru <tmgn_at_excite.com>
Date: Tue, 21 Sep 1999 13:59:39 -0400
Message-ID: <37E7C78B.27A9E24E@excite.com>

No it doesnt cause Data loss as you fear. Redo Log Buffer Cache is a Circular Buffer and the LGWR process writes the new Redo Entries in any of the following conditions :

1. Once every 3 seconds
2. when 1/3 rd of the LoG_BUffers is Full
3. When the DBWR has to write the modified buffers,if necessary (LGWR uses

write-ahead protocol)

Since Commit confirmation is given to the USer process only after the corresponding redo entries are written to the Online Redo Log files(which may be used for Recovery), no Commited Data is lost .

Any Uncommitted transactions are Rolled Back during Instance recovery..

Hope this helps..

-Thiru

Magnus Bergh wrote:

> hI am not so sure about how the log_buffer parameter works. Does the
> buffer work as a cache (wait to write until log buffer is full or some
> other criteria) or is it used to avoid wait when the LGWR process is busy
> writing to log files.
>
> if log buffers is used as a cache, couldn't this cause data loss if the
> Oracle instance crash? Then all buffers in the cache would be lost. I
> hope and don't think it is this way, but I want to be sure.
>
> Magnus
Received on Tue Sep 21 1999 - 12:59:39 CDT