Out of memory during index creation

Hello,

PG version 8.4.7 on AIX 6.1.
While creating a large multi-column index on a table of about 2.5 million rows, I got the following error:
ERROR: out of memory
DETAIL: Failed on request of size 50331648.

I doubled the value of the "shared_buffers" parameter (from 512Mb to 1024Mb), recycled the PG instance and then was able to run the "create index" statement successfully.

Question: Does PG use a main memory sort algorithm for the creation of indexes? Can it not make do with whatever memory is available and supplement it with disk space (external sort)? I have a temporaray tablespace defined (with the "temp_tablespaces") parameter. The disk area for this tablespace had about 2GB of free space available. But the sort does not seem to have used it.

Thanks.

Alanoly Andrews.

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