| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: overestimate on empty table |
| Date: | 2017-11-11 17:43:04 |
| Message-ID: | 4000.1510422184@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> On Fri, Nov 10, 2017 at 04:19:41PM -0500, Tom Lane wrote:
>> One idea is to say that relpages = reltuples = 0 is only the state that
>> prevails for a freshly-created table, and that VACUUM or ANALYZE should
>> always set relpages to at least 1 even if the physical size is zero.
>> Dunno if that would confuse people.
> What about adding && rel->rd_rel->reltuples==0, and make VACUUM/ANALYZE instead
> set only reltuples=1, since that's already done at costsize.c: clamp_row_est()
> and therefor no additional confusion?
1 tuple in 0 pages is a physically impossible situation, so I'm quite
sure that way *would* confuse people.
regards, tom lane
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