Re: shared-memory based stats collector - v70

On Wed, 20 Jul 2022 at 12:08, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> AFAIR, the previous stats collector implementation had no such provision
> either: it'd just keep adding hashtable entries as it received info about
> new objects. The only thing that's changed is that now those entries are
> in shared memory instead of process-local memory. We'd be well advised to
> be sure that memory can be swapped out under pressure, but otherwise I'm
> not seeing that things have gotten worse.

Just to be clear I'm not looking for ways things have gotten worse.
Just trying to understand what I'm reading and I guess I came in with
assumptions that led me astray.

But... adding entries as it received info about new objects isn't the
same as having info on everything. I didn't really understand how the
old system worked but if you had a very large schema but each session
only worked with a small subset did the local stats data ever absorb
info on the objects it never touched?

All that said -- having all objects loaded in shared memory makes my
work way easier. It actually seems feasible to dump out all the
objects from shared memory and including objects from other databases
and if I don't need a consistent snapshot it even seems like it would
be possible to do that without having a copy of more than one stats
entry at a time in local memory. I hope that doesn't cause huge
contention on the shared hash table to be doing that regularly.

--
greg