Re: O(n) tasks cause lengthy startups and checkpoints

On 12/13/21, 12:37 PM, "Robert Haas" <robertmhaas(at)gmail(dot)com> wrote:
> On Mon, Dec 13, 2021 at 1:21 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
>> > But against all that, if these tasks are slowing down checkpoints and
>> > that's avoidable, that seems pretty important too. Interestingly, I
>> > can't say that I've ever seen any of these things be a problem for
>> > checkpoint or startup speed. I wonder why you've had a different
>> > experience.
>>
>> Yeah, it's difficult for me to justify why users should suffer long
>> periods of downtime because startup or checkpointing is taking a very
>> long time doing things that are arguably unrelated to startup and
>> checkpointing.
>
> Well sure. But I've never actually seen that happen.

I'll admit that surprises me. As noted elsewhere [0], we were seeing
this enough with pgsql_tmp that we started moving the directory aside
before starting the server. Discussions about handling this usually
prompt questions about why there are so many temporary files in the
first place (which is fair). FWIW all four functions noted in my
original message [1] are things I've seen firsthand affecting users.

Nathan

[0] https://postgr.es/m/E7573D54-A8C9-40A8-89D7-0596A36ED124%40amazon.com
[1] https://postgr.es/m/C1EE64B0-D4DB-40F3-98C8-0CED324D34CB%40amazon.com