| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Dilip Kumar <dilipbalaut(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Performance degradation in Bitmapscan (commit 75ae538bc3168bf44475240d4e0487ee2f3bb376) |
| Date: | 2017-01-06 16:01:32 |
| Message-ID: | CA+TgmoYQC4yB=DROdSsZUzS5TUpPtHZVwtX7W9BsoX+cWtpizQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Jan 6, 2017 at 10:43 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2016-12-16 09:34:31 -0800, Andres Freund wrote:
>> > To fix his issue, we need something like your 0001. Are you going to
>> > polish that up soon here?
>>
>> Yes.
>
> I've two versions of a fix for this. One of them basically increases the
> "spread" of buckets when the density goes up too much. It does so by
> basically shifting the bucket number to the left (e.g. only every second
> bucket can be the "primary" bucket for a hash value). The other
> basically just replaces the magic constants in my previous POC patch
> with slightly better documented constants. For me the latter works just
> as well as the former, even though aesthetically/theoretically the
> former sounds better. I'm inclined to commit the latter, at least for
> now.
Did you intend to attach the patches?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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