| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Magnus Hagander <magnus(at)hagander(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: shared-memory based stats collector |
| Date: | 2018-07-06 19:34:43 |
| Message-ID: | CA+TgmoYbd9h3cisB_=p=ASg9o_vJm8rmW7VZs-TS0Mu947AxtQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Jul 6, 2018 at 3:02 PM, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> Will stats, if we move toward the suggested changes be "less" accurate than
> they are now? We already know that stats are generally not accurate but they
> are close enough. If we move toward this change will it still be close
> enough?
There proposed change would have no impact at all on the long-term
accuracy of the statistics. It would just mean that there would be
race conditions when reading them, so that for example you would be
more likely to see a count of heap scans that doesn't match the count
of index scans, because an update arrives in between when you read the
first value and when you read the second one. I don't see that
mattering a whole lot, TBH, but maybe I'm missing something.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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