Re: Increase in 'log file sync' waits while 'log file parallel write' remains unchanged

From: vsevolod afanassiev <>
Date: Mon, 21 Sep 2009 16:52:33 -0700 (PDT)
Message-ID: <>

> Do you have available cpu time on this system when the log file waits
> shoot up?

This is LPAR on big AIX p595 frame, it has 32 CPU.

> Unless you are showing some signs of severe cpu starvation ( that
> might have been missed possibly ) I think you gotta check out the IO
> subsystem.

> My databases get about .5 ms for log file sync ... 10 ms is ugly and
> 100 ms just ouch.

'log file sync' is wait experienced by foreground user process while 'log file parallel write'
is wait event experienced by Log Writer. I thought that slow I/O will lead to increase
in 'log file parallel write'.

I checked db once agai, found that log_buffer is set to 1MB. If we unset it the
default value will be 4 MB (128K * cpu_count), I don't think it will help.

> Local storage or SAN?  Can you get some iostat information during the
> bad times?

Yes, this is EMC DMX-something (2000). Received on Mon Sep 21 2009 - 18:52:33 CDT

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