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Re: Index build temp files

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Index build temp files
Date: 2013-01-09 00:04:32
Message-ID: 5417.1357689872@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Bruce Momjian (bruce(at)momjian(dot)us) wrote:
>> Well, our docs for temp_tablespaces says:
>> This variable specifies tablespaces in which to create temporary
>> objects (temp tables and indexes on temp tables) when a
>> <command>CREATE</> command does not explicitly specify a tablespace.
>> Temporary files for purposes such as sorting large data sets
>> are also created in these tablespaces.
>> 
>> Are you saying this is inaccorate?

> Yes and no?  Are the temporary files created during a CREATE INDEX
> considered "Temporary files for purposes such as sorting large data
> sets"?  My thinking is 'yes', but others may disagree.  Also,
> considering this a bug would imply that it's back-patchable and I'm not
> convinced it's worth the risk of breaking things which depend on the
> current behavior.

I don't think it's a bug.  What you seem to be proposing is that CREATE
INDEX ought to ignore temp_tablespaces and instead always put its temp
files in the tablespace where the finished index will reside.  This
would not be a good idea IMO --- allowing the temp files to be spread to
other tablespaces is better both from the standpoint of space usage and
the ability to overlap I/O.  (Admittedly, both of those concerns are
often theoretical, but if they are then I don't see why you'd care which
tablespace is used.)

			regards, tom lane


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Subject: Re: Index build temp files
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