Re: O_DIRECT and performance

> 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
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