[postgis-users] Help with Bad Query Plan
mark.cave-ayland at siriusit.co.uk
Thu Jan 8 12:48:12 PST 2009
Oliver Snowden wrote:
> Dear all, I am having some problems with a bad query plan. Essentially,
> I have two tables. A table of many different types of geography and
> another table (reports) linking to those geographies. We want to select
> a small subset of reports (e.g. 30 reports) based on date and intersect
> those report geographies (potentially historical geographies) with a
> (current) selected geography.
> I have (conceptually) worked out what I believe to be most efficient by
> putting the query into canonical form, moving the restricts down and
> putting the most restrictive item first; although I haven't actually
> done any specific calculations - index/disk access speeds etc.
> My view is that the query should be executed as shown below.
> Any comments or suggestions will be greatly appreciated. We have tried
> various things inc. subqueries, using &&, and indexing almost everything
> etc. Still no luck.
> Many thanks, Oliver.
Please can we see the EXPLAIN ANALYZE output for queries STEP 3 and STEP 4?
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