From: Noah Misch <noah@leadboat.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Ronan Dunklau <ronan.dunklau@aiven.io>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: pgsql-bugs <pgsql-bugs@lists.postgresql.org>
Subject: Re: FSM Corruption (was: Could not read block at end of the relation)
Date: Thu, 11 Apr 2024 19:27:08 -0700
Message-ID: <20240412022708.d6@rfd.leadboat.com> (raw)
In-Reply-To: <CAH2-Wzm8tWR8fEgPTQ+BB-Wqt+efHso-vNfmCKr06ZmiLpjbNQ@mail.gmail.com>
References: <VtPLBUerbMM8BSDLQwIMV9Co_38iHS1TXE4V09x2ZVFhPkZMNE8LwgPSIzB8PHkVFXykGx04QNAzZVjJFAnU1w==@protonmail.internalid>
<1970118.yKVeVyVuyW@aivenlaptop>
<20240312220807.05.nmisch@google.com>
<3225659.5fSG56mABF@aivenlaptop>
<20240313165523.6a@rfd.leadboat.com>
<CAH2-Wzm8tWR8fEgPTQ+BB-Wqt+efHso-vNfmCKr06ZmiLpjbNQ@mail.gmail.com>
On Thu, Apr 11, 2024 at 12:01:09PM -0400, Peter Geoghegan wrote:
> On Wed, Mar 13, 2024 at 12:55 PM Noah Misch <noah@leadboat.com> wrote:
> > That's a reasonable thing to worry about. We could do wrong by trying too
> > hard to use an FSM slot, and we could do wrong by not trying hard enough.
>
> Although it's not related to the problem you're working on, it seems
> like a good opportunity to bring up a concern about the FSM that I
> don't believe was discussed at any point in the past few years: I
> wonder if the way that fsm_search_avail() sometimes updates
> fsmpage->fp_next_slot with only a shared lock on the page could cause
> problems. At the very least, it's weird that we allow it.
fsm_search_avail() treats an out-of-range fp_next_slot like zero, so I'm not
seeing a correctness issue. I bet changing it under an exclusive lock
wouldn't deliver better-optimized searches to an extent that pays for the
synchronization overhead, but it might.
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To: pgsql-bugs@postgresql.org
Cc: noah@leadboat.com, pg@bowt.ie, ronan.dunklau@aiven.io, michael@paquier.xyz, pgsql-bugs@lists.postgresql.org
Subject: Re: FSM Corruption (was: Could not read block at end of the relation)
In-Reply-To: <20240412022708.d6@rfd.leadboat.com>
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