Re: shared buffers and startup process

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On Tue, Jan 14, 2020 at 04:29:51PM +0100, Joao Junior wrote:
> I would like to know if  increasing the amount of shared-buffers could help
> the startup process applying the wals. I would like to know if in
> the process of reading the wals and applying them,  blocks that should be
> written will be  brought to shared buffer or not??

Please feel free to look at XLogReadBufferForRedo() in xlogutils.c and
check what the routine does, and when/where it gets called.  The code
is well-documented, so you will find your answer easily.

> If yes, having a bigger
> shared buffer will keep as much as possible the amount of pages there and
> increase the startup process's speed avoiding pages's replacement and going
> to the OS cache and maybe to the disk .
> Does it make sense?

It does.  Even if relying on the OS cache would be enough in most
cases, it is good to keep a certain of pages hot enough, and you need
to be careful with not setting shared_buffers too high either.
--
Michael

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