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

On Fri, Jan 6, 2017 at 11:06 AM, Andres Freund <andres@anarazel.de> wrote:
> On 2017-01-06 11:01:32 -0500, Robert Haas wrote:
>> 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?
>
> No, I hadn't. You're interested in the "spreading" version?

I honestly have no opinion.  If you're confident that you know what
you want to do, it's fine with me if you just do it.  If you want my
opinion I probably need to see both patches and compare.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company