Re: [HACKERS] Performance degradation in Bitmapscan (commit 75ae538bc3168bf44475240d4e0487ee2f3bb376)

On Fri, Jan 6, 2017 at 10:43 AM, Andres Freund <andres@anarazel.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
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