| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, vadim4o(at)email(dot)com |
| Subject: | Re: WAL and commit_delay |
| Date: | 2001-02-17 18:46:22 |
| Message-ID: | 4356.982435582@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> With the delay, it looks like:
> time backend 1 backend 2
> ---- --------- ---------
> 0 write()
> 1 sleep() write()
> 2 fsync() sleep()
> 3 fsync()
Actually ... take a close look at the code. The delay is done in
xact.c between XLogInsert(commitrecord) and XLogFlush(). As near
as I can tell, both the write() and the fsync() will happen in
XLogFlush(). This means the delay is just plain broken: placed
there, it cannot do anything except waste time.
Another thing I am wondering about is why we're not using fdatasync(),
where available, instead of fsync(). The whole point of preallocating
the WAL files is to make fdatasync safe, no?
regards, tom lane
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