| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Melanie Plageman <melanieplageman(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: lazy_scan_heap() should release lock on buffer before vacuuming FSM |
| Date: | 2023-11-15 23:17:18 |
| Message-ID: | 20231115231718.y7l72jk5vxsj6dck@awork3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2023-11-15 16:32:48 -0500, Robert Haas wrote:
> On Mon, Nov 13, 2023 at 8:26 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > I think this undersells the situation a bit. We right now do
> > FreeSpaceMapVacuumRange() for 8GB of data (VACUUM_FSM_EVERY_PAGES) in the main
> > fork, while holding an exclusive page level lock.
>
> That sounds fairly horrific?
It's decidedly not great, indeed. I couldn't come up with a clear risk of
deadlock, but I wouldn't want to bet against there being a deadlock risk.
I think the rarity of it does ameliorate the performance issues to some
degree.
Thoughts on whether to backpatch? It'd probably be at least a bit painful,
there have been a lot of changes in the surrounding code in the last 5 years.
- Andres
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