Postgres Pro
Downloads
Home   >   mailing lists

Re: lazy_scan_heap() should release lock on buffer before vacuuming FSM - Mailing list pgsql-hackers

From Andres Freund
Subject Re: lazy_scan_heap() should release lock on buffer before vacuuming FSM
Date
Msg-id 20231115231718.y7l72jk5vxsj6dck@awork3.anarazel.de
Whole thread Raw
In response to Re: lazy_scan_heap() should release lock on buffer before vacuuming FSM  (Robert Haas <robertmhaas@gmail.com>)
Responses Re: lazy_scan_heap() should release lock on buffer before vacuuming FSM
List pgsql-hackers
Tree view 
Hi,

On 2023-11-15 16:32:48 -0500, Robert Haas wrote:
> On Mon, Nov 13, 2023 at 8:26 PM Andres Freund <andres@anarazel.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

pgsql-hackers by date:

Previous
From: Tom Lane
Date:
Subject: Re: WaitEventSet resource leakage
Next
From: Roberto Mello
Date:
Subject: Re: Add minimal C example and SQL registration example for custom table access methods.