Re: Same query doing slow then quick

Here is the answer to Ray Stell who send me the wiki page of Slow Query. I
hope i detailed all you wanted (i basicly pasted the page and add my
answers).

Full Table and Index Schema:

schema tables_adresses
"Tables"
tables_adresses.adresses_XX (id (serial), X(Double precision),Y (Double
precision)).
"Indexes"
adresses_XX_pkey (Primary key, btree)
calcul_XX (non unique, Btree on X,Y)

schema tables_gps
"Tables"
tables_gps.gps_XX (id (int),x_max(numeric(10,5)), y_max
(numeric(10,5)),x_min(numeric(10,5)),y_min(numeric(10,5)))
"Indexes"
calculs_XX (non unique Btree x_min,x_max,y_min,y_max)
gps_10_pkey (Primary key on id btree)

Approximate rows 250000.
No large objects in it (just data)
No NULL
receives a large number of UPDATEs or DELETEs regularly
is growing daily

I can't post an EXPLAIN ANALYZE because of the 6hour query time.

Postgres version: 9.1

History: was this query always slow, : "YES"

Hardware: Ubuntu server last version 32bits

Daily VACUUM FULL ANALYZE, REINDEX TABLE on all the tables.

WAL Configuration: Whats a WAL ?

GUC Settings: i didn't change anything. All is standard.

shared_buffers should be 10% to 25% of available RAM (it's on 24MB and can't
go higher. The server has 4Gb)

effective_cache_size should be 75% of available RAM => I don't now what this
is.

Test changing work_mem: increase it to 8MB, 32MB, 256MB, 1GB. Does it make a
difference? "No"

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