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Trying to create multi db query in one large queries

From: Hasnul Fadhly bin Hasan <hasnulfadhly(dot)h(at)mimos(dot)my>
To: pgsql-performance(at)postgresql(dot)org
Subject: Trying to create multi db query in one large queries
Date: 2004-12-14 01:44:56
Message-ID: 41BE4598.2040708@mimos.my (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

I am not sure if this is the place to ask this question, but since the 
question is trying to improve the performance.. i guess i am not that 
far off.

My question is if there is a query design that would query multiple 
server simultaneously.. would that improve the performance?

To make it clear.. let's say we have 3 db servers.  1 server is just 
designed to take the queries while the other 2 server is the ones that 
actually
holds the data.  let's say we have a query of 'select * from 
customer_data' and we change it to
select * from
(
dblink('db1','select * from customer_data where timestamp between 
timestamp \'01-01-2004\' and timestamp \'06-30-2004\'')
union
dblink('db2','select * from customer_data where timestamp between 
timestamp \'01-07-2004\' and timestamp \'12-31-2004\'')
)

Would the subquery above be done simultaneously by postgres before doing 
the end query? or would it just execute one at a time?

If it does execute simultaneously.. it's possible to create code to 
convert normal queries to distributed queries and requesting data from 
multiple
database to improve performance.  This would be advantageous for large 
amount of data.

Thanks,

Hasnul



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