I have a server with 4GB of RAM and PostgreSQL 9.0.3 on Centos 5. I'm using pgbench and pgbench-tools to measure performance, using two pgbench-tools queries: select and tpc-b.
With default settings of postgresql.conf and select query, I get the following results:
I don't understand why when the scale is 100 or more in the second benchmark, the performance is so low compared to the first test. The only thing I have done was increase the memory.
I've thrown every test twice and the results were similar. In an earlier test, the memory configuration was:
And the results were similar, even slightly worse. For that reason, I did tests changing options one by one, to know what was the cause of poor performance. And "the winner" is shared_buffers...