Right - if you split a table to a lot of more selective tables, it can often
dramatically change the plan options (e.g. - in a single table, selectivity
for a query may be 1% and require an expensive nested loop while in the more
restrictive table it may match 14% of the data and do a cheaper scan).

Also - don't forget that just rebuilding a database cleanly can dramatically
improve performance.

The only dbms I know that indexes views is MS SQL Server 2000, where it is a
limited form of materialized queries. pg doesn't do MQs, but check out
functional indices.


----- Original Message ----- 
From: "Gregory S. Williamson" <[EMAIL PROTECTED]>
To: "Igor Maciel Macaubas" <[EMAIL PROTECTED]>;
Sent: Thursday, October 14, 2004 2:45 PM
Subject: Re: [PERFORM] Performance vs Schemas


I'm not sure if it is proper to state that schemas are themselves speeding
things up.

As an example, we have data that is usually accessed by county; when we put
all of the data into one big table and select from it using a code for a
county of interest, the process is fairly slow as there are several hundred
thousand candidate rows from that county in a table with many millions of
rows. When we broke out certain aspects of the data into schemas (one per
county) the searches become very fast indeed because we can skip the
searching for a specific county code with the relevant tables and there is
less (unneeded) data in the table being searched.

As always, "EXPLAIN ANALYZE ..." is your friend in understanding what the
planner is doing with a given query.

See <http://www.varlena.com/varlena/GeneralBits/Tidbits/> for some useful
information, especially under the performance tips section.


Greg Williamson
GlobeXplorer LLC

-----Original Message-----
From: Igor Maciel Macaubas [mailto:[EMAIL PROTECTED]
Sent: Thu 10/14/2004 11:38 AM
Subject: [PERFORM] Performance vs Schemas
Hi all,

I recently migrated my database from schema 'public' to multiple schema.
I have around 100 tables, and divided them in 14 different schemas, and then
adapted my application to use schemas as well.
I could percept that the query / insert / update times get pretty much
faster then when I was using the old unique schema, and I'd just like to
confirm with you if using schemas speed up the things. Is that true ?

What else I can do to speed up the query processing, best pratices,
recommendations ... ? What about indexed views, does postgresql supports it?


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