Re: PATCH: Split stats file per database WAS: autovacuum stress-testing our system

Dne 06.02.2013 16:53, Alvaro Herrera napsal:
> Tom Lane escribió:
>> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> >> Nice. Another interesting numbers would be device utilization,
>> average
>> >> I/O speed and required space (which should be ~2x the pgstat.stat
>> size
>> >> without the patch).
>>
>> > this point is important - with large warehouse with lot of
>> databases
>> > and tables you have move stat file to some ramdisc - without it
>> you
>> > lost lot of IO capacity - and it is very important if you need
>> only
>> > half sized ramdisc
>>
>> [ blink... ] I confess I'd not been paying close attention to this
>> thread, but if that's true I'd say the patch is DOA. Why should we
>> accept 2x bloat in the already-far-too-large stats file? I thought
>> the idea was just to split up the existing data into multiple files.
>
> I think they are saying just the opposite: maximum disk space
> utilization is now half of the unpatched code. This is because when
> we
> need to write the temporary file to rename on top of the other one,
> the
> temporary file is not of the size of the complete pgstat data
> collation,
> but just that for the requested database.

Exactly. And I suspect the current (unpatched) code ofter requires more
than
twice the space because of open file descriptors to already deleted
files.

Tomas