|From:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|To:||Andres Freund <andres(at)anarazel(dot)de>|
|Cc:||David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>|
|Subject:||Re: Speed up transaction completion faster after many relations are accessed in a transaction|
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2019-02-18 19:01:06 -0500, Tom Lane wrote:
>> Mmm ... AIUI, the patches currently proposed can only help for what
>> David called "point lookup" queries. There are still going to be
>> queries that scan a large proportion of a partition tree, so if you've
>> got tons of partitions, you'll be concerned about this sort of thing.
> Agreed - but it seems not unlikely that for those the rest of the
> planner / executor overhead will entirely swamp any improvement we could
> make here. If I understand correctly the benchmarks here were made with
> "point" update and select queries, although the reference in the first
> post in this thread is a bit vague.
I think what Maumau-san is on about here is that not only does your
$giant-query take a long time, but it has a permanent negative effect
on all subsequent transactions in the session. That seems worth
doing something about.
>> I didn't say it had to be a constant ...
> Do you have good idea?
I think David's on the right track --- keep some kind of moving average of
the LOCALLOCK table size for each transaction, and nuke it if it exceeds
some multiple of the recent average. Not sure offhand about how to get
the data cheaply --- it might not be sufficient to look at transaction
end, if we release LOCALLOCK entries before that (but do we?)
regards, tom lane
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