| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Luca Ferrari <fluca1978(at)gmail(dot)com> |
| Cc: | pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: statistic target and sample rate |
| Date: | 2021-07-14 14:30:29 |
| Message-ID: | 3484552.1626273029@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Luca Ferrari <fluca1978(at)gmail(dot)com> writes:
> Therefore my question is about how the statistic collectore decides
> about the number of tuples to be sampled.
It's basically 300 times the largest statistics target:
Per that comment, there is good math backing this choice for the task
of making a histogram. It's a little shakier for other sorts of
statistics --- notably, for n_distinct estimation, the error can still
be really bad.
regards, tom lane
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