| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
| Cc: | Michael Lewis <mlewis(at)entrata(dot)com>, Israel Brewster <ijbrewster(at)alaska(dot)edu>, PostgreSQL Mailing Lists <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Faster distinct query? |
| Date: | 2021-09-22 20:48:42 |
| Message-ID: | 2228441.1632343722@sss.pgh.pa.us |
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| Lists: | pgsql-general |
"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> There is no where clause so I'm doubtful there is much to be gained going
> down this path. The Index-Only scan seems like an optimal way to obtain
> this data and the existing query already does that.
The "index-only" scan is reported to do 86m heap fetches along the
way to returning 812m rows, so the data is apparently pretty dirty.
It's possible that a preliminary VACUUM to get page-all-visible hint
bits set would be a net win.
regards, tom lane
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