Re: increasing the default WAL segment size

On 25 August 2016 at 02:31, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> Furthermore, there is an enforced, synchronous fsync at the end of
> every segment, which actually does hurt performance on write-heavy
> workloads.[2] Of course, if that were the only reason to consider
> increasing the segment size, it would probably make more sense to just
> try to push that extra fsync into the background, but that's not
> really the case. From what I hear, the gigantic number of files is a
> bigger pain point.

I think we should fully describe the problem before finding a solution.

This is too big a change to just tweak a value without discussing the
actual issue.

And if the problem is as described, how can a change of x4 be enough
to make it worth the pain of change? I think you're already admitting
it can't be worth it by discussing initdb configuration.

If we do have the pain of change, should we also consider making WAL
files variable length? What do we gain by having the files all the
same size? ISTM better to have WAL files that vary in length up to 1GB
in size.

(This is all about XLOG_SEG_SIZE; I presume XLOG_BLCKSZ can stay as it
is, right?)

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services