On 9/6/19, 10:26 AM, "Robert Haas" <robertmhaas@gmail.com> wrote:
> On Thu, Sep 5, 2019 at 4:08 PM Bossart, Nathan <bossartn@amazon.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