| From: | Greg Sabino Mullane <htamfids(at)gmail(dot)com> |
|---|---|
| To: | Jon Zeppieri <zeppieri(at)gmail(dot)com> |
| Cc: | pgsql-performance(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Why a bitmap scan in this case? |
| Date: | 2024-12-19 18:38:57 |
| Message-ID: | CAKAnmmL327t5MRJ2uonQ3JB5bLegRbfa-WtpaTNBnbJ1iVef5Q@mail.gmail.com |
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| Lists: | pgsql-performance |
>
> Why wouldn't it do an index (or, really, an index only) scan in this case
Well, it did do an index scan (and a bitmap scan is a pretty good solution
here), but as to why no indexonly scan, there is probably not enough
assurance that it won't have to hit the heap heavily anyway. Try doing a
SET enable_bitmapscan=0; and re-run with EXPLAIN ANALYZE. If you see a
large number of "Heap Fetches", that could be why. Vacuum the table and try
again after doing SET enable_bitmapscan=1;
Cheers,
Greg
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