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Re: ASM mirroring, which is good?
- From: Andreas Piesk <a.piesk@xxxxxxx>
- To: ag@xxxxxxxxxxxx
- Date: Tue, 03 Jul 2007 18:36:41 +0200
Alex Gorbachev schrieb:
Can you elaborate on this? I would be surprised to see any significant
performance degradation. Is that those intermittent delays of few
hundred ms you mentioned?
yes, i can give some details.
i noticed delays (log file sync wait event) up to 2500ms while writing
to redo logs. normally a log file sync completes in less than 20ms
because the SAN is very fast due to a big write cache of several GBs.
a database transaction == business transaction has a size of approx.
4-5K and contains a LOB of 3.5K.
it's very difficult to trace because of it's intermittent nature. i
suppose, ASM locks while updating it's meta data when, for example,
registering a new extent, but i cannot prove it.
for testing i put the redologs on raw devices mirrored by AIX cLVM onto
the same SAN boxes. i got very good log file sync times with no large
delays (< 100ms) even with maximum load on the database.
so it seems ASM is somehow involved but the proof is not easy. the
performance drop is not significant because it does not happen very
often but it is a bit annoying.
i haven't the chance to test 10.2.0.3 on AIX because i'm still waiting
for patches from 10.2.0.2 ported to 10.2.0.3.
regards,
-ap
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