| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Use of index for 50% column restriction |
| Date: | 2016-06-14 21:35:00 |
| Message-ID: | 20160614213500.GB15349@momjian.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Tue, Jun 14, 2016 at 03:24:12PM -0500, Jim Nasby wrote:
> On 6/8/16 4:36 PM, Bruce Momjian wrote:
> >Just a follow-up, but even with a randomized correlation order, it seems
> >25% restrictivity generates a Bitmap Index Scan:
>
> AFAIK we do the bitmap heap scan in heap order, thereby eliminating the
> effect of correlation?
High correlation would still cause us to access fewer heap pages than
random data.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Merlin Moncure | 2016-06-14 21:58:44 | Re: 10.0 |
| Previous Message | Jim Nasby | 2016-06-14 21:15:27 | Re: 10.0 |