Re: [ADMIN] pg_class reltuples/relpages not updated by autovacuum/vacuum

2011/5/25 Alvaro Herrera <alvherre@commandprompt.com>:
> Excerpts from Kevin Grittner's message of mié may 25 12:37:24 -0400 2011:
>> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>> > I don't know what client-side code might be looking at
>> > relpages/reltuples.
>>
>> I know that I find reltuples useful for getting an "accurate enough"
>> sense of rows in a table (or set of tables) without resorting to
>> count(*).  I'd be OK with any two of pages, tuples, and density; but
>> dropping to one would make databases harder to manage, IMV.
>>
>> Personally, I don't have much code that uses those columns;
>> eliminating an existing column wouldn't involve much pain for me as
>> long as it could still be derived.
>
> Well, we only actually need to store one number, because you can figure
> out a much more precise number-of-pages figure with pg_relation_size()
> divided by configured page size.
>
> (We feel free to hack around catalogs in other places, and we regularly
> break pgAdmin and the like when we drop columns -- people just live with
> it and update their tools.  I don't think it's such a big deal in this
> particular case.)

I may miss something but we need relation size in costsize.c even if
we have a reldensity (or we need a reltuples). Else what values should
be used to estimate the relation size ? (pg_relation_size() goes down
to kernel/fs to ask the stat.st_size, is it really what we want?)


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