Why is PostgreSQL so slow on Windows?

Question

We had an applicationg running using MySql. We found MySql was not suitable for our app after we found that it didnt support some of the GIS capability that PostGIS has (note: m

Answer 1

There are cases where PostgreSQL on Windows pays an additional overhead compared to other solutions, due to tradeoffs made when we ported it.

For example, PostgreSQL uses a process per connection, MySQL uses a thread. On Unix, this is usually not a noticeable performance difference, but on Windows creating new processes is very expensive (due to the lack of the fork() system call). For this reason, using persistent connections or a connection pooler is much more important on Windows when using PostgreSQL.

Another issue I've seen is that early PostgreSQL on Windows will by default make sure that it's writes are going through the write cache - even if it's battery backed. AFAIK, MySQL does not do this, and it will greatly affect write performance. Now, this is actually required if you have a non-safe hardware, such as a cheap drive. But if you have a battery-backed write cache, you want to change this to regular fsync. Modern versions of PostgreSQL (certainly 8.3) will default to open_datasync instead, which should remove this difference.

You also mention nothing about how you have tuned the configuration of the database. By default, the configuration file shipped with PostgreSQL is very conservative. If you haven't changed anything there, you definitely need to take a look at it. There is some tuning advice available on the PostgreSQL wiki.

To give any more details, you will have to provide a lot more details about exactly what runs slow, and how you have tuned your database. I'd suggest an email to the pgsql-general mailinglist.