[pgpool-general: 1254] The performance is not proportional to the number of backend hosts

Jonas Hsiao jonash at synology.com
Wed Dec 12 18:40:20 JST 2012


I am using pgpool for load balancing. However, the results of pgbench are
not as good as I thought.
Even though the statements are all SELECT.

The command of pgbench I used is as follows:
$ pgbench -p 9999 -h  -t 100 -c 1000 -j 1 -Sr -U admin testdb

Under observation, I found the session activities are weird by typing
following command.
$ ps | grep pgpool | grep -c SELECT

When pgpool only connects to ONE backend host. The number of SELECT
sessions is about 100~130 when pgbench is running.
But there are only 10~13 if THREE backend hosts are connected.
Although the TPS(transactions per second) measured by pgbench is about 1.3
times better than the one which only a backend host connected.
The performance is still not satisfied, it should be THREE times better!

BTW, the CPU utilization in backend host is about 90% when one backend host
connected; only 30% when three backend hosts connected.
The memory and I/O seems fine.

How can I further improve the performance ?
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