From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Joe Conway <mail(at)joeconway(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
Subject: | Re: stawidth inconsistency with all NULL columns |
Date: | 2019-05-21 20:54:25 |
Message-ID: | 4897.1558472065@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Joe Conway <mail(at)joeconway(dot)com> writes:
> On 5/21/19 3:55 PM, Tom Lane wrote:
>> Are you suggesting that we should set stawidth to zero even for a
>> fixed-width datatype? That seems pretty silly. We know exactly what
>> the value should be, and would be if we'd chanced to find even one
>> non-null entry.
> Well you could argue in similar fashion for variable width values -- if
> we find even one of those, it will be at least 4 bytes. So why set those
> to zero?
Um, really the minimum width is 1 byte, given short headers. But as
the code notes, zero means we don't know what a sane estimate would
be, which is certainly not the case for fixed-width types.
regards, tom lane
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