On 23.12.2005, at 15:35 Uhr, Carlos Benkendorf wrote:
I appreciate your suggestion but I think I´m misunderstanding something, the select statement should return at about 150.000 rows, why 5 rows?
I have looked at the wrong lines of the explain ... statement. Sorry, my fault. With that many lines, I doubt that my workaround will do anything good ... :-/ I was just a little bit to fast ... looking at to many different "explain ..." (or similar) statements in the last weeks.
Sorry, my fault.Other idea: have you tried ordering the rows in memory? Is that faster? From now looking better at the explain result, it seems to me, that the sorting takes most of the time:
Sort (cost=201296.59..201663.10 rows=146602 width=897) (actual time=9752.555..10342.363 rows=167710 loops=1)
How large are the rows returned by your query? Do they fit completely in the memory during the sort? If PostgreSQL starts switching to temp files ... There was a discussion on that topic a few weeks ago ...
Perhaps this may help: ------------------------------ work_mem (integer)Specifies the amount of memory to be used by internal sort operations and hash tables before switching to temporary disk files. The value is specified in kilobytes, and defaults to 1024 kilobytes (1 MB). Note that for a complex query, several sort or hash operations might be running in parallel; each one will be allowed to use as much memory as this value specifies before it starts to put data into temporary files. Also, several running sessions could be doing such operations concurrently. So the total memory used could be many times the value of work_mem; it is necessary to keep this fact in mind when choosing the value. Sort operations are used for ORDER BY, DISTINCT, and merge joins. Hash tables are used in hash joins, hash-based aggregation, and hash-based processing of IN subqueries.
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