| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Daniel Caune" <daniel(dot)caune(at)ubisoft(dot)com> |
| Cc: | "Andrew Sullivan" <ajs(at)crankycanuck(dot)ca>, pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: How to force PostgreSQL using an index |
| Date: | 2006-02-15 22:47:15 |
| Message-ID: | 20471.1140043635@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
"Daniel Caune" <daniel(dot)caune(at)ubisoft(dot)com> writes:
> SELECT <some-columns>
> FROM GSLOG_EVENT
> WHERE EVENT_NAME = 'player-status-update'
> AND EVENT_DATE_CREATED >= <start-time>
> AND EVENT_DATE_CREATED < <end-time>
> I have an index on EVENT_DATE_CREATED that does it job. But I though
> that I can help my favourite PostgreSQL if I create a composite index on
> EVENT_DATE_CREATED and EVENT_NAME (in that order as EVENT_DATE_CREATED
> is more dense that EVENT_NAME).
Wrong ... should be EVENT_NAME first. Think about the sort order of the
data to see why --- your query represents a contiguous subset of the
index if EVENT_NAME is first, but not if EVENT_DATE_CREATED is first.
regards, tom lane
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