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Re: Lots and lots of redo logs

From: Paul Drake <>
Date: Tue, 18 Sep 2001 21:53:44 -0700
Message-ID: <>

Bill Buchan wrote:
> Out of curiosity and as a test I scrubbed my 16Mb RAID1 array and set it up
> again with 5 x 50Mb redo groups. I ran the following script to generate
> lots of redo:
> begin
> for i in 1..15000000 loop
> insert into test_table values (mod(i,10));
> delete from test_table where anumber = (mod(i+1,10));
> commit;
> end loop;
> end;
> ARCHIVELOG mode was on and the archive destination (on another disk) was
> initially empty.
> There were 239 log switches and the test completed in 2 hours 56 minutes.
> I then added a further 250 50Mb redo groups, cleared the archive
> destination and ran the test again. Again it completed in exactly 2 hours
> 56 minutes, this time 240 log switches (difference of 1, I guess due to
> whereabouts in the first log it was when the test started).
> v$session_wait shows permanent "log file parallel write" for LGWR while the
> test runs.
> Any suggestions why I failed to see any slow down when I (almost) filled
> the disk with redo groups? (This server wasn't doing anything else and the
> time of the test). The RAID1 array had a Linux ext2 filesystem on it and I
> had disabled the write cache.
> Thanks again,
> - Bill.


Is there any chance that you had the following:

It seems likely that the bottleneck was not in the LGWR process. As others here would likely indicate, what were the other I/O-related v$system_event waits?

Since I don't see version info, is it possible that you do not have a dedicated CKPT process?


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Author: Paul Drake

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Received on Tue Sep 18 2001 - 23:53:44 CDT

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