Parallel queries for a web-application |performance testing

From: Balkrishna Sharma
Subject: Parallel queries for a web-application |performance testing
Date: ,
Msg-id: BAY149-w5365651952D598741FE4E1F0DE0@phx.gbl
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Responses: Re: Parallel queries for a web-application |performance testing  ("Kevin Grittner")
Re: Parallel queries for a web-application |performance testing  (Dimitri Fontaine)
Re: Parallel queries for a web-application |performance testing  (Matthew Wakeling)
List: pgsql-performance


Hello,
I will have a web application having postgres 8.4+ as backend. At any given time, there will be max of 1000 parallel web-users interacting with the database (read/write)
I wish to do performance testing of 1000 simultaneous read/write to the database.

I can do a simple unix script on the postgres server and have parallel updates fired for example with an ampersand at the end. Example:

echo '\timing \\update "DAPP".emp_data set f1 = 123where  emp_id =0;' | "psql" test1 postgres|grep "Time:"|cut -d' ' -f2- >> "/home/user/Documents/temp/logs/$NUM.txt" &
pid1=$!   
echo '\timing \\update "DAPP".emp_data set f1 = 123 where  emp_id =2;' | "psql" test1 postgres|grep "Time:"|cut -d' ' -f2- >> "/home/user/Documents/temp/logs/$NUM.txt" &
pid2=$!    
echo '\timing \\update "DAPP".emp_data set f1 = 123 where  emp_id =4;' | "psql" test1 postgres|grep "Time:"|cut -d' ' -f2- >> "/home/user/Documents/temp/logs/$NUM.txt" &
pid3=$!    
.......
......


My question is:
Am I losing something by firing these queries directly off the server and should I look at firing the queries from different IP address (as it would happen in a web application). Would the way postgres opens sockets/allocates buffer etc change in the two approaches and I get non-realistic results by a unix script on the server ?
It will be very tedious  exercise to have 1000 different machines (IP address)  and each firing a query; all the same time. But at the same time, I want to be absolutely sure my test would give the same result in production (requirements for latency for read/write is very very low)
I am not interested in the network time; just the database read/write time.


Thanks for any tips !
-Bala


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From: "Kevin Grittner"
Date:
Subject: Re: Parallel queries for a web-application |performance testing
From: "jgardner@jonathangardner.net"
Date:
Subject: Re: PostgreSQL as a local in-memory cache