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List:       opensolaris-dtrace-discuss
Subject:    [dtrace-discuss] fdsync takes looong
From:       Paul van den Bogaard <Paul.VandenBogaard () Sun ! COM>
Date:       2008-07-11 9:59:00
Message-ID: 25001145.1215795668981.JavaMail.Twebapp () oss-app1
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Running a PostgreSQL database and trying to understand the bottleneck in my setup. I \
now know there is a fdsync being issued to a database file. This one takes up to 10 \
seconds.  The problem here is that all the other processes are entering a wait state \
(this is in postgres itself. The syncing process holds a latch in exclusive mode, \
that is needed by all others) waiting for this flush to finish. All my 128+ processes \
accumulate 10 seconds, throttling my throughput for a total of 1280 seconds. This is \
significant! There is definitely a relation with the database checkpoints that when \
happening consequently make the long fdsync show up.

I would like to delve in a little deeper. It could be the sheer number of pages that \
are being written due the fdsycn. Wonder if someone has a dtrace script snippet I \
could use here to understand a little better what is going on under the hood.

BTW running ZFS where my intent log is on a RAID array which has 1GB of write caches. \


Thanks,
Paul


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