Re: fsync vs open_sync

pgsql(at)mohawksoft(dot)com writes:
> The improvements were REALLY astounding, and I would like to know if other
> Linux users see this performance increase, I mean, it is almost 8~10 times
> faster than using fsync.
> Furthermore, it seems to also have the added benefit of reducing the I/O
> storm at checkpoints over a system running with fsync off.

What size transactions are you using in your tests?

For a system with small transactions (not much more than 1 page worth of
WAL traffic per transaction) I'd be pretty surprised if there was any
real difference at all. There certainly should not be any difference in
terms of the number of physical writes. We have seen some platforms
where fsync() is inefficiently implemented and requires more kernel
overhead than is reasonable --- not for I/O, but just to look through
the kernel buffers and confirm that none of them need flushing. But I
didn't think Linux was one of these.

regards, tom lane