| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Bill Moran <wmoran(at)collaborativefusion(dot)com> |
| Cc: | Jim Nasby <decibel(at)decibel(dot)org>, Postgresql list Performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Fragmentation of WAL files |
| Date: | 2007-04-26 15:37:42 |
| Message-ID: | 24354.1177601862@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
> In response to Jim Nasby <decibel(at)decibel(dot)org>:
>> I was recently running defrag on my windows/parallels VM and noticed
>> a bunch of WAL files that defrag couldn't take care of, presumably
>> because the database was running. What's disturbing to me is that
>> these files all had ~2000 fragments.
It sounds like that filesystem is too stupid to coalesce successive
write() calls into one allocation fragment :-(. I agree with the
comments that this might not be important, but you could experiment
to see --- try increasing the size of "zbuffer" in XLogFileInit to
maybe 16*XLOG_BLCKSZ, re-initdb, and see if performance improves.
The suggestion to use ftruncate is so full of holes that I won't
bother to point them all out, but certainly we could write more than
just XLOG_BLCKSZ at a time while preparing the file.
regards, tom lane
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