I'm trying to port our application from MS-SQL to Postgres. We have implemented all of our rather complicated application security in the database. The query that follows takes a half of a second or less on MS-SQL server and around 5 seconds on Postgres. My concern is that this data set is rather "small" by our applications standards. It is not unusual for the da_answer table to have 2-4 million records. I'm worried that if this very small data set is taking 5 seconds, then a "regular sized" data set will take far too long.
I originally thought the NOT EXISTS on the "da_data_restrict_except_open" table was killing performance, but the query took the exact same amount of time after I deleted all rows from this table. Note that the hard-coded 999999999.0, and 4000 parameters, as well as the parameter to svp_getparentproviders are the three variables that change from one run of this query to the next.
I'm using Postgres 7.4.5 as packaged in Debian. shared_buffers is set to 57344 and sort_mem=4096.
That shared_buffers value sounds too large for 1GB RAM - rewind to 10000 say. Also make sure you've read the "performance tuning" article at:
http://www.varlena.com/varlena/GeneralBits/Tidbits/index.php
I have included an EXPLAIN ANALYZE, relevant table counts, and relevant indexing information. If anyone has any suggestions on how to improve performance.... TIA!
I think it's the function call(s).
SELECT tab.answer_id, client_id, question_id, recordset_id,...
date_effective, virt_field_name
FROM
(
SELECT a.uid AS answer_id, a.client_id, a.question_id, recordset_id,
date_effective
FROM da_answer a
WHERE a.date_effective <= 9999999999.0
AND a.inactive != 1
AND
(
5000 = 4000 OR
(EXISTS (SELECT * FROM svp_getparentproviderids(1) WHERE
svp_getparentproviderids = a.provider_id))
)
SubPlan
-> Function Scan on svp_getparentproviderids (cost=0.00..15.00 rows=5
width=4) (actual time=0.203..0.203 rows=0 loops=21089)
Filter: (svp_getparentproviderids = $1)
Here it's running 21,089 loops around your function. Each one isn't costing much, but it's the total that's killing you I think. It might be possible to mark the function STABLE or such, depending on what it does - see http://www.postgresql.org/docs/7.4/static/sql-createfunction.html
-- Richard Huxton Archonet Ltd
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