RE: Archived redo log size difference in 10gR2

Hi,

This is because the multiple private redolog strands in 10g.

As each of the private redolog strands is protected by a separate redo allocation latch (e.g. there is no single point of serialization for protecting physical log space allocation), the space for private redolog strands has to be pre-reserved. This helps to avoid overcommitting space in current redolog group (as that would mess up RBA addresses because RBA has log sequence number in it).

This space is just reserved from total size of current redolog group. The amount to reserve is recalculated every logswitch - if Oracle decides to dynamically increase the number of private strands on logswitch, it may reserve more space for them in new current redolog group.

If any of the reserved space is unused when its time to switch the log (e.g. all of the "unreserved" space has been used up), then the generated archivelog will be smaller by the unused reserved amount of space (as there's no point in doing blank padding like the metalink note mentioned).

There are few _log_private% parameters which control the amount of space allocated per active session but generally there's no need to tune these - just make your redolog groups big.

Tanel.

> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jesse, Rich
> Sent: Wednesday, November 01, 2006 03:49
> To: oracle-l
> Subject: Archived redo log size difference in 10gR2
>
> Hey all,
>
> We're well on our way to implementing a new ERP system in
> 10.2.0.2.0 on AIX 5.3. One thing I've noticed is that while
> the redo logs are ~50MB, the archived redo logs from
> "regular" log switches are consistently only ~45MB. On
> 9.2.0.5 on HPUX, our 90MB redos tend to switch with 2K free.
>
> Not that this affects a whole lot in my planning, but I'm
> just curious.
> Trapsing through the admin docs doesn't seem to mention
> anything other than the minimum size of a log is 4MB.
>
> Thoughts anyone? And if you have definitive info, where from?
>
> TIA,
> Rich
> --
> http://www.freelists.org/webpage/oracle-l
>
>

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