Re: FYI: fdatasync vs sync_file_range

On Mon, 2009-07-06 at 17:54 +0900, Fujii Masao wrote:

> According to the result, using sync_file_range instead of fdatasync
> has little effect in the performance of postgres.

["...when flushing XLOG"]

Why did you think it would?

AFAICS the range of dirty pages will be restricted to a fairly tight
range anyway. The only difference between the two would indicate an OS
inefficiency. I don't see an opportunity for XLOG to be more efficient
by using a finer-grained API.

I think there is still a valid use for sync_file_range at checkpoint,
since the for some large tables this could reduce the number of pages
needing to be written at checkpoint time. That would help smooth out
larger writes.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support