From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Small performance regression in 9.2 has a big impact |
Date: | 2014-11-25 23:02:22 |
Message-ID: | 24181.1416956542@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> writes:
> On Tue, Nov 25, 2014 at 1:58 PM, Heikki Linnakangas
> <hlinnakangas(at)vmware(dot)com> wrote:
>> I don't know why this regressed between those versions, but looking at the
>> functions, there's some low-hanging fruit:
>>
>> 1. tree_ancestor_keys() could use UNION ALL instead of UNION. (I believe
>> duplicates are expected here, although I'm not 100% sure).
>>
>> 2. tree_ancestor_keys() calculates tree_level($1) every time it recurses.
>> Would be cheaper to calculate once, and pass it as argument.
> Wow that made a huge difference. About a 50% increase across the
> board. Sadly, 9.2 is still way behind 8.4 (see Tom's email)
Switching from UNION to UNION ALL would dodge the varbit hash-opclass
caching issue, I think. But there's still something else going on.
regards, tom lane
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