From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Tatsuo Ishii <ishii(at)postgresql(dot)org> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: planstats.sgml |
Date: | 2016-02-16 00:00:42 |
Message-ID: | 15174.1455580842@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Tatsuo Ishii <ishii(at)postgresql(dot)org> writes:
> While reading planstats.sgml, I encounted a sentence which I don't
> understand.
> These numbers are current as of the last <command>VACUUM</> or
> <command>ANALYZE</> on the table. The planner then fetches the
> actual current number of pages in the table (this is a cheap operation,
> not requiring a table scan). If that is different from
> <structfield>relpages</structfield> then
> <structfield>reltuples</structfield> is scaled accordingly to
> arrive at a current number-of-rows estimate. In this case the value of
> <structfield>relpages</structfield> is up-to-date so the rows estimate is
> the same as <structfield>reltuples</structfield>.
> I don't understand the last sentence (In this case...). For me it
> seems it is talking about the case when replages is not different from
> what the planner fetches from the table. If so, why "In this case"?
I think what it meant is "In the example above, ...". Feel free to
change it if you think that is clearer.
regards, tom lane
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