Re: archivelog performance issues
Date: Tue, 7 Jul 2009 13:25:26 -0700
> On Tue, Jul 7, 2009 at 12:23 PM, Richard Croasmun <rac_oracledba_at_msn.com
> > wrote:
> ...I would say that all the points about log size, frequency of
> log switches, number of online logs etc would apply even when the DB
> is NOT in archive log mode. The only exception would be having
> enough online logs (or large enough logs) such that the copy of a
> particular log finishes before the database wants to use that online
> redo log again. ... Am I missing anything here?
On Jul 7, 2009, at 10:42 AM, Andrew Kerber wrote:
> Uh, Yes. If you are not in archive log mode, the redo log is not
> copied to the archivelog, so there is no overhead on the switch.
> When you are not in archive log mode, you just switch to the next
> redo log and keep going, overwriting what was in the log previously.
I think some of the "overhead" people have been mentioning includes the cost of log switch checkpoint, which rightly or wrongly, drives some of the effort to size logs for switching at particular intervals. I agree that the greatest possible detractor from performance with archivelog mode is log copy. To determine if archivelog mode has any performance impact, the measurement should be whether 'log file parallel write' time for LGWR increases when ARCn are writing.
Blue Gecko, Inc.