This is interesting.
http://www-128.ibm.com/developerworks/db2/library/techarticle/dm-0603wasserman2/
There are a few bugs
1. In the graphic overview PostgreSQL == Progres
2. In description of PostgreSQL database cluster, "After
initialization, a database cluster contains a database called
postgres, which is a default database used by utilities, users and
third party applications. " That doesn't seem to be necessarily true.
I don't have that database....
3. He misses the fact that some configuration options can be set
interactively via SET
4. "The VACUUM command must be run on a regular basis to recover disk
space occupied by updated or deleted rows and to update data
statistics used by the PostgreSQL query planner. " with no mention of
autovacuum. He is talking about 8.1.
Every time I learn about a big commercial database I am amazed at how
much 'bigger' and more complicated than PostgreSQL they are - I guess
they have to be for their intended use - and how similar to PostgreSQL
they are in actual function.