From: | Harshad <harshad(dot)rj(at)gmail(dot)com> |
---|---|
To: | pgsql-novice(at)postgresql(dot)org |
Subject: | Reason for PG being seemingly I/O bound? |
Date: | 2009-09-13 17:00:18 |
Message-ID: | h8j892$sdg$1@ger.gmane.org |
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Lists: | pgsql-novice |
Hi,
I am trying to figure out why a very simple query turns out to be I/O bound. (I have spent more than 2 days
learning and tweaking everything from "shared_buffer" to "vm.swappiness", but not making any progress.)
The postgresql.conf is set to all defaults.
The table is called 'users' which has an INTEGER id with a UNIQUE constraint.
There are only about 1000 rows in the table.
The query and the plan is:
EXPLAIN
SELECT null
FROM users
WHERE id=14601448;
QUERY PLAN
----------------------------------------------------------------------
Index Scan using "userId" on users (cost=0.00..8.27 rows=1 width=0)
Index Cond: (id = 14601448)
I have put this query in simple.sql, and running it in a tight loop in the shell thusly:
while [ true ] ; do psql -d twinkle -U postgres -f simple.sql; done > /dev/null
(that's zsh syntax; in bash it would be while [[ true ]] ...)
The CPU utilisation of this is hardly 5%.
I have tried this on my PC as well as the production server, with several combinations of configuration settings
(including the defaults, shutting off autovacumm, shutting off synchronised_commit, shutting off fsync, etc).
What am I missing?
thanks for your help,
Harshad
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