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Why is UseDeclareFetch so slow?

From: Rainer Bauer <usenet(at)munnin(dot)com>
To: pgsql-odbc(at)postgresql(dot)org
Subject: Why is UseDeclareFetch so slow?
Date: 2007-06-22 15:06:11
Message-ID: (view raw or whole thread)
Lists: pgsql-odbc

based on the problem I had here
I thought it would be interesting to know why UseDeclareFetch is slowing my
query down dramatically.

I have a table containing 50 tuples and retrieve all 50 tuples with a bound
column select statement:
SELECT * FROM tblItem WHERE intItemIDCnt = ?

This takes 8 seconds (over a slow DSL connection with 150ms ping). Tom Lane
suggested enabling UseDeclareFetch and the performance drop was significant:
Instead of 8 seconds, the query now takes 30-32 seconds. I also tested
enabling UseServerSidePrepare (without UseDeclareFetch) and the query was
executed in 7 seconds.

After rewriting the query to use an IN clause it now works perfect:
SELECT * FROM tblItem WHERE intItemIDCnt IN (...)
The result is retrieved in 400ms (UseServerSidePrepare=950ms and

The only thread I found discussing the UseDeclareFetch/UseServerSidePrepare
options was <>.

So my questions are
1) Is there any chance the driver itself could be enhanced like Dimitri
suggested here:
2) When should UseServerSidePrepare be used?
3) When should UseDeclareFetch be used?



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