Re: Optimizer's issue

On Thu, 24 Apr 2008, Vlad Arkhipov wrote:
> It was written below in my first post:
> "These queries are part of big query and optimizer put them on the leaf
> of query tree, so rows miscount causes a real problem. "
> actual rows count for the first query is 294, estimate - 11; for the
> second -- 283 and 0. Postgres tries to use nested loops when it should
> use merge/hash join and vice versa.

The queries are taking less than three milliseconds. You only have three
hundred rows in each table. The precise algorithm Postgres uses probably
won't make much of a difference. Have you tried turning off the relevant
join plans to see how long Postgres takes with your desired plan?

When you have millions of rows, the algorithm matters a lot more.

Matthew

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