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Message-ID: <20041111170050.75735.qmail@web53501.mail.yahoo.com>
Date: Thu, 11 Nov 2004 09:00:50 -0800 (PST)
From: jing han <jing_han_66@yahoo.com>
Subject: about libpq-C FETCH performance issue
To: pgsql-interfaces@postgresql.org
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Hello,

I'm working on a project where libpq-C is envolved. We
have several background processes keep querying
certain data from database to send out ip packets at
fast rate.

With libpq-C interface, I use 

res = PQexec(conn, "DECLARE myportal CURSOR FOR select
* from ourTables");

and then  res = PQexec(conn, "FETCH ALL in myportal");


to get the data. 

I found when our database has more and more data, res
= PQexec(conn, "FETCH ALL in myportal"); cost more and
more time, much more than 

res = PQexec(conn, "DECLARE myportal CURSOR FOR select
* from ourTables"); 

(note:ourTables can be several tables join together)

and make our sending packet rate extremely low. We get
into big problems here. 

Then I try FETCH 1 instead of FETCH ALL, no
improvement.

All the queries our background processes use was
optimized with EXPLAIN utility, these queries take
much shorter time in postgres console.

So I wonder what FETCH statement is doing: just fetch
query results from cursor or do the real query, get
the query result and give these results to us. Why it
is much slower than console sql command?

I wonder if there is other faster way ( I mean other
than FETCH ALL command) to get data from database with
libpq-C, or If you have a patch to make FETCH work
faster?

Hope to hear from you soon.


Best Regards
jing

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