[postgis-users] Postgresql not using Spatial Index

[dblasby at openplans.org]

>Have you tried setting the effective_cache_size parameter for your
laptop as
>well? This is used to calculate how many tuples are cached outside of
shared
>buffers (i.e. incur very little disk I/O). I generally find setting
>effective_cache_size correctly and reducing random_page_cost to 2
solves
>nearly all index problems.

Maybe this is more of a postgresql issue than a postgis issue - I
certainly shouldnt have to modify my configuation so it doesnt make
asinine (15:1) query plans! I know that I dont want to have to modify
my underlying configuration; new-to-intermediate users almost certainly
dont want to do that!

The PostGIS install should be (1) install PostGIS (2) update your
configuration.

I think it would be far better to have the PostGIS estimator return a
better cost estimate - that way everyone wins.

>I also seem to remember reading somewhere on -hackers recently that 5%
was
>the fixed threshold between index and sequential scans (determined by
>PostgreSQL), but I can't find a reference to it in the archives at the
>moment.

I thought postgresql would look at the estimates and choose the
lowest-cost one.

dave



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