Re: [BUGS] General Bug Report: Files greater than 1 GB are created while sorting

Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> I have renamed these sort temp tables to pg_sorttemp so they will not be
> confused with actual temp tables.

I didn't realize that the names generated for temp tables were so close
to those generated for temp files. Changing one or the other does seem
like a good idea. But I do not like "pg_sorttemp" because fd.c's
temporary-file mechanism is used for more things than just sorting.
Hash joins, for example. Can we think of a better name?

Alternatively, how about including the user-given name for a temp table
into its real name? That would be helpful for debugging, I'm sure.
I'm thinking of something like

snprintf(newrelname, NAMEDATALEN, "pg_temp.%d.%u.%s",
(int) MyProcPid, uniqueId++, userrelname);

(relying on snprintf to truncate the user name if too long, here).

> You are safe up to 2 gigs, and at that point, the OS will can cause a
> problem. The new naming should make the cause clearer. Don't know if
> we can get this done in 6.5.1 because the change to segment these
> requires some work. Looks like the psort code goes right to fd/*,
> bypassing the storage manager.

Yes, it will take some thought to figure out how to handle multi-segment
temp files without cluttering the code too badly. I think it can be
handled inside fd.c, though.

Note that under ordinary circumstances, the data being processed by a
sort or hash join will be written into several temp files that each get
just a fraction of the data; so you would not actually see a problem
until you got to several-times-2-Gig total data volume.

regards, tom lane