Re: Disappointing performance in db migrated from MS SQL Server

Leon,

> Hello all. I am in the midst of porting a large web application from a
> MS SQL Server backend to PostgreSQL. The migration work is basically
> complete, and we're at the testing and optimization phase of the
> project. The results so far have been disappointing, with Postgres
> performing queries in about the same time as SQL Server even though
> Postgres is running on a dedicated box with about 4 times the clock
> speed of the SQL Server box. For a chart of my results, please see
> http://leonout.com/pggraph.pdf for a graph of some test results.

Your settings look ok to start, but we'll probably want to tune them further.
Can you post some details of the tests?   Include:

1) the query
2) the EXPLAIN ANALYZE results of the query
3) Whether you ran the test as the only connection, or whether you tested
multi-user load.

The last is fairly important for a SQL Server vs. PostgreSQL test; SQL Server
is basically a single-user-database, so like MySQL it appears very fast until
you get a bunch o' users on it.

Finally, for most queries the disk I/O and the RAM are more important than the
CPU clock speed.   From the looks of it, you upgraded the CPU + RAM, but did
downgraded the disk array as far as database writes are concered; not a
terrible effective way to gain performance on your hardware.

--
-Josh Berkus
 Aglio Database Solutions
 San Francisco