[postgis-users] Tuning

[dblasby at openplans.org]

Guillaume SUEUR (Géosignal) wrote:

>For most of the types it's ok, but when I try to display the heaviest
one >(street, 1400000 rows), the map generation is very long (about 40
>seconds), even using a close scale (10000, less than 20 streets are
then >displayed.

This usually happens when you didnt 'analyse' the table.  Analyse does
some simple statistics that the SQL statement optimizer needs to know
in order to make an efficient query plan.

# analyse <table name>;  --- does one table
# analyse;  -- does entire database  (I think - check the documentation)

Wen you find a query that's really slow, you should ask postgresql what
query plan it's using:

# EXPLAIN ANAYSE <your query>;

It will execute the query, and compare its estimates vs what actually
happened.

dave

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