From: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
---|---|
To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | "Schneider, Jeremy" <schnjere(at)amazon(dot)com>, "pgsql-bugs(at)postgresql(dot)org" <pgsql-bugs(at)postgresql(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, "Nasby, Jim" <nasbyj(at)amazon(dot)com> |
Subject: | Re: ERROR: multixact X from before cutoff Y found to be still running |
Date: | 2019-09-17 19:34:45 |
Message-ID: | 090A11C7-9EA5-4D78-93B2-99E0D6C2BC0E@amazon.com |
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Lists: | pgsql-bugs pgsql-hackers |
On 9/6/19, 10:26 AM, "Robert Haas" <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Sep 5, 2019 at 4:08 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
>> Right, the v2 patch will effectively ramp-down the freezemin as your
>> freeze_max_age gets smaller, while the v1 patch will set the effective
>> freezemin to zero as soon as your multixact age passes the threshold.
>> I think what is unclear to me is whether this ramp-down behavior is
>> the intended functionality or we should be doing something similar to
>> what we do for regular transaction IDs (i.e. force freezemin to zero
>> right after it hits the "oldest xmin is far in the past" threshold).
>> The comment above MultiXactMemberFreezeThreshold() explains things
>> pretty well, but AFAICT it is more geared towards influencing
>> autovacuum scheduling. I agree that v2 is safer from the standpoint
>> that it changes as little as possible, though.
>
> I don't presently have a view on fixing the actual but here, but I can
> certainly confirm that I intended MultiXactMemberFreezeThreshold() to
> ratchet up the pressure gradually rather than all at once, and my
> suspicion is that this behavior may be good to retain, but I'm not
> sure.
Thanks for the detailed background information. FWIW I am now in
favor of the v2 patch.
Nathan
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