| From: | Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Gould <daveg(at)sonic(dot)net>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Alina Alexeeva <alexeeva(at)adobe(dot)com>, Ullas Lakkur Raghavendra <lakkurra(at)adobe(dot)com> |
| Subject: | Re: [patch] BUG #15005: ANALYZE can make pg_class.reltuples inaccurate. |
| Date: | 2018-03-01 16:56:20 |
| Message-ID: | 1386effe-0e6d-fd5a-6f0d-f294e4ef2dda@postgrespro.ru |
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| Lists: | pgsql-hackers |
On 01.03.2018 18:09, Tom Lane wrote:
> Ideally, at least, the estimate would remain on-target.
The test shows that under this particular scenario the estimated number
of tuples grows after each ANALYZE. I tried to explain how this happens
in the attached pdf. The direct averaging of the number of tuples, not
using the density, doesn't have this problem, so I suppose it could help.
> I think you're reinventing the way we used to do it. Perhaps consulting
> the git history in the vicinity of this code would be enlightening.
I see that before vac_estimate_reltuples was introduced, the results of
analyze and vacuum were used directly, without averaging. What I am
suggesting is to use a different way of averaging, not to remove it.
--
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
| Attachment | Content-Type | Size |
|---|---|---|
| analyze.tex.pdf | application/pdf | 57.9 KB |
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