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help / color / mirror / Atom feedFrom: Tom Lane <tgl@sss.pgh.pa.us>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: overestimate on empty table
Date: Sat, 11 Nov 2017 12:43:04 -0500
Message-ID: <4000.1510422184@sss.pgh.pa.us> (raw)
In-Reply-To: <20171111171945.GA2167@telsasoft.com>
References: <20171110204043.GS8563@telsasoft.com>
<9772.1510348781@sss.pgh.pa.us>
<20171111171945.GA2167@telsasoft.com>
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Justin Pryzby <pryzby@telsasoft.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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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, pryzby@telsasoft.com
Subject: Re: overestimate on empty table
In-Reply-To: <4000.1510422184@sss.pgh.pa.us>
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