Re: query optimization

Richard Kojedzinszky <krichy@tvnetwork.hu> writes:
> Dear list,
> We have a database schema, which looks the same as the attached script.

> When filling the tables with data, and skipping analyze on the table (so
> pg_stats contains no records for table 'a'), the first select in the
> script runs fast, but after an analyze the planner decides to sequence
> scan tables b and c, thus making the query much slower. Can somebody help
> me solving this issue, or tuning our installation to not to use sequence
> scans in this case?

Um ... did you analyze all the tables, or just some of them?  I get
sub-millisecond runtimes if all four tables have been analyzed, but it
does seem to pick lousy plans if, say, only a and b have been analyzed.

What you really need for this query structure is the parameterized-path
work I've been doing for 9.2; but at least on the exact example given,
I'm not seeing that 9.1 is that much worse.

            regards, tom lane