Thank you for your post. I finally spent some quality time with the query planner section in the docs' server config chapter. Very instructive, even considering that most of it went over my head!
...have you got effective_cache_size set to something that's realistic for your machine?
I guess not. It was the default value (128MB) on a machine with 4GB of RAM. It's not a dedicated server, though, so I'll set it to 1G for now.
But before doing so I need a clarification. The docs state that this parameter is used only for cost estimation, and has no effect on actual memory allocations. I imagine that if other memory-related settings are not somehow in line with it, it could lead to estimates that are out of touch with reality. If this is correct what other memory-related parameters do I need to adjust to ensure that both the planner's estimates and the actual execution agree and fit well with the available memory?
One problem with this test is that your smaller tables probably fit in
memory whereas the big ones may not, so it's not a given that your test
accurately reflects how the real query will go down.
That's a very helpful reminder. Thanks.
Kynn