From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
Cc: | Michael Paquier <michael(at)paquier(dot)xyz>, Andres Freund <andres(at)anarazel(dot)de>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "sulamul(at)gmail(dot)com" <sulamul(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: inefficient loop in StandbyReleaseLockList() |
Date: | 2021-10-31 19:38:15 |
Message-ID: | 1013797.1635709095@sss.pgh.pa.us |
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"Bossart, Nathan" <bossartn(at)amazon(dot)com> writes:
> On 10/28/21, 11:53 PM, "Michael Paquier" <michael(at)paquier(dot)xyz> wrote:
>> Actually, as the list of recovery locks is saved in TopMemoryContext,
>> wouldn't it be better to keep a per-cell deletion of the list, which
>> would mean that we'd better do the operation in the reverse order to
>> make things faster with the new list implementation? But that's what
>> Andres points at with CFIs in the middle of one list of the hash table
>> processed?
> Hm. IIUC anything bad enough to cause the startup process to break
> out of the StandbyReleaseLockList() loop will also cause the entire
> process to be restarted. I'm not seeing any risk of reusing a half-
> released lock list. I might be misunderstanding the concern, though.
Yeah, there's no expectation that this data structure needs to be kept
consistent after an error; and I'm not real sure that the existing
code could claim to satisfy such a requirement if we did need it.
(There's at least a short window where the caller's hash table entry
will point at an already-freed List.)
Pushed the patch as given. I've not yet reviewed other list_delete_first
callers, but I'll take a look. (I seem to remember that I did survey
them while writing 1cff1b95a, but I evidently missed that this code
could be dealing with a list long enough to be problematic.)
regards, tom lane
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