Re: hashagg slowdown due to spill changes

From: Andres Freund <andres(at)anarazel(dot)de>
To: pgsql-hackers(at)lists(dot)postgresql(dot)org,Jeff Davis <pgsql(at)j-davis(dot)com>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: hashagg slowdown due to spill changes
Date: 2020-06-11 17:45:25
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On June 10, 2020 6:15:39 PM PDT, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>On Fri, 2020-06-05 at 21:11 -0700, Andres Freund wrote:
>> Hi,
>> While preparing my pgcon talk I noticed that our hash-agg performance
>> degraded noticeably. Looks to me like it's due to the spilling-
>> hashagg
>> changes.
>Attached a proposed fix. (Might require some minor cleanup).
>The only awkward part is that LookupTupleHashEntry() needs a new out
>parameter to pass the hash value back to the caller. Ordinarily, the
>caller can get that from the returned entry, but if isnew==NULL, then
>the function might return NULL (and the caller wouldn't have an entry
>from which to read the hash value).


Did you run any performance tests?

Sent from my Android device with K-9 Mail. Please excuse my brevity.

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