2011/5/25 Alvaro Herrera <alvherre@commandprompt.com>:
> Excerpts from Cédric Villemain's message of mié may 25 13:24:01 -0400 2011:
>
>> > 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.
>
>> 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?)
>
> Actually yes, the planner does go to kernel to determine the current
> relation size, and then multiplies by density as computed from catalog
> data to figure out current reasonably accurate number of tuples.
Okay! I just read that part. Interesting.
(If I dive correctly, we search our last segment and then use a
fileseek to the end of this segment to get our information)
make more sense, suddendly :)
>
> --
> Álvaro Herrera <alvherre@commandprompt.com>
> The PostgreSQL Company - Command Prompt, Inc.
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>
--
Cédric Villemain 2ndQuadrant
http://2ndQuadrant.fr/ PostgreSQL : Expertise, Formation et Support
