| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Shaun Thomas <sthomas(at)optionshouse(dot)com> |
| Cc: | "Andrew W(dot) Gibbs" <awgibbs(at)awgibbs(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: query against large table not using sensible index to find very small amount of data |
| Date: | 2014-04-08 22:51:46 |
| Message-ID: | CAMkU=1wXAoZFdNmh43B+RvmsG4RfmPXaMLqi+imU81WWFSw_cA@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
On Tue, Apr 8, 2014 at 6:39 AM, Shaun Thomas <sthomas(at)optionshouse(dot)com>wrote:
>
> > Other possibly relevant pieces of information... The entity type
> > column has a cardinality in the neighborhood of a couple dozen.
> > Meanwhile, for some of the entity types there is a large and ongoing
> > number of events, and for other entity types there is a smaller and
> > more sporadic number of events. Every now and again a new entity
> > type shows up.
>
> With that as the case, I have two questions for you:
>
> 1. Why do you have a low cardinality column as the first column in an
> index?
>
Because if he didn't have it, the planner would never be able to use it.
Remember, the problem is when the planner chooses NOT to use that index.
Cheers,
Jeff
| From | Date | Subject | |
|---|---|---|---|
| Next Message | uher dslij | 2014-04-09 00:16:30 | Re: Performance regressions in PG 9.3 vs PG 9.0 |
| Previous Message | Tom Lane | 2014-04-08 21:26:37 | Re: Performance regressions in PG 9.3 vs PG 9.0 |