Re: [PERFORM] Two fast queries get slow when combined

cluster <skrald@amossen.dk> writes:
> Queries and output from EXPLAIN ANALYZE can be seen here with some
> syntax highlighting:
> http://rafb.net/p/BJIW4p69.html

You are lying to us about how those queries were posed to Postgres (and no I don't feel a need to explain how I know). In future please present the full truth about what you are doing, not a simplification that you think is sufficient.

But I think the short answer to your question is that query 1 is fast because it need only select the first 50 rows in some ordering, and query 2 is fast because it need only select the first 50 rows in some ordering, but they are not the same ordering so the join query doesn't get to exploit that shortcut.

                        regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
       subscribe-nomail command to majordomo@postgresql.org so that your
       message can get through to the mailing list cleanly