RE: buffer writes vs. archived logs generation

Patrice,

Didn't see any answers from the performance gurus, so here's my take on this.

While it is true that all changes that are made to the database is made against the buffers in the buffer cache, this is preceded by redo entries in the redo buffer that is in turn written almost continuosly into the redologs. It is these redologs that are then written out as archivelogs at redolog switch (when a redolog fills up). Multiple changes to a particular 'hot' db buffer will result in multiple redolog entries (more redolog and thus archive log) but a single write (buffer write) when the buffer is ultimately written out. In other words, the amount of information written out as measured by 'buffer writes' cannot be compared to archivelogs generated when you have a multiple simultaneous update-intensive workload. I believe you should look at V$SYSSTAT's 'redo blocks written' to measure what you are looking for.

Does this answer your query? Btw, what did you use to measure 'buffer writes'?

John Kanagaraj
Oracle Applications DBA
DBSoft Inc
(W): 408-970-7002

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• The opinions and statements above are entirely my own and not those of my employer or clients **

> -----Original Message-----
> From: Boivin, Patrice J [mailto:BoivinP_at_mar.dfo-mpo.gc.ca]
> Sent: Monday, January 14, 2002 7:35 AM
> To: Multiple recipients of list ORACLE-L
> Subject: buffer writes vs. archived logs generation
>
>
> FYI,
>
> I just compared audit trail data for buffer writes against
> the number of
> archived logs generated per day.
>
> Although there appears to be a vague correspondence between
> the two, it is
> not always the case.
>
> I would have thought that the relationship would have been
> more direct.
>
> Would anyone know why some buffer writes might not get
> written through redo
> logs?
>
> Regards,
> Patrice Boivin
> Systems Analyst (Oracle Certified DBA)
>
> Systems Admin & Operations | Admin. et Exploit. des systèmes
> Technology Services | Services technologiques
> Informatics Branch | Direction de l'informatique
> Maritimes Region, DFO | Région des Maritimes, MPO
>
> E-Mail: boivinp_at_mar.dfo-mpo.gc.ca
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> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Boivin, Patrice J
> INET: BoivinP_at_mar.dfo-mpo.gc.ca
>
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: John Kanagaraj
  INET: john.kanagaraj_at_hds.com

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