From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Doug McNaught <doug(at)wireboard(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: O_DIRECT and performance |
Date: | 2001-09-28 00:40:17 |
Message-ID: | 200109280040.f8S0eHM23002@candle.pha.pa.us |
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Lists: | pgsql-hackers |
> Well, O_DIRECT has finally made it into the Linux kernel. It lets you
> open a file in such a way that reads and writes don't go to the buffer
> cache but straight to the disk. Accesses must be aligned on
> filesystem block boundaries.
>
> Is there any case where PG would benefit from this? I can see it
> reducing memory pressure and duplication of data between PG shared
> buffers and the block buffer cache. OTOH, it does require that writes
> be batched up for decent performance, since each write has an implicit
> fsync() involved (just as with O_SYNC).
>
> Anyone played with this on systems that already support it (Solaris?)
I have heard there are many cases there O_DIRECT on Solaris is slower
for databases than normal I/O. I think bulk copy was faster but not
normal operation. Probably not something we are going to get into soon.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
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