Jon, When planning the introduction of computing technology, the choice of products and the resulting architecture is rarely a cut and dried exercise. It isn't just a case of selecting best of breed components and plugging them in. Often competing solutions have slightly different features or performance characteristics. Sometimes one requires more in the way of support than another. Sometimes the skills for one choice are readily at hand and the most critical consideration is the completion date.

That said, MySQL seems to perform more quickly in the trivial case—applicatons where the database stores information used only to serve Web pages and the data structure is rather basic. PostgreSQL has more features to control referential integrity and build more ambitious databases both in size and complexity. Just as a large corporation may use Oracle or DB2 for its business data and SQL-Server for its Web site, I expect there are enterprises that use both PostgreSQL and MySQL.

As for expensive commercial products vs. their low-cost open-source rivals, many large and well-known enterprises rely entirly on open-source products to support aspects of their businesses. Netcraft regularly polls over 7.75 million active Web sites. Their latest report indicates that 61.88% use the free, open-source Apache Web server and that number is rising. Only 26.4% use Microsoft's IIS Web server and their market share has been falling since September. That may be due to the increased emphasis on security.

A few other sites I checked from Netcraft are listed below:

• Yahoo.com runs on FreeBSD and MySQL.
• Amazon.com runs on Linux and the Apache Web server.
• The U.S. White House site runs on Linux.
• The IBM site runs Apache on AIX and I assume their DBMS is DB2.
• The Univ. of Calif. at Berkeley runs Apache on Red Hat Linux using PHP and OpenSSL.

Here is an article that appeared last July on the TechRepublic site called “What to consider when moving from MySQL to PostgreSQL.” It presents a good outline of the differences between the two.

Here is an article that discusses NASA's switch to MySQL from Oracle.

I think database systems like SQL-Server and MySQL have a shorter learning curve and are more popular with developers who don't have to worry about building enterprise class applications. Still, I don't know of anyone trying to run SAP on PostgreSQL. When they spend millions of dollars for the hardware they tend to go for commercial database products as well. Enterprise applications often need to be “highly available” so the DBMS must be able to fail over automatically to a standby system as well.

At the same time SAP AG is pushing their proprietary database product out into open-source under the GNU license.

Here is a Computerworld article talking about the growing popularity of open-source DBMS products.

This one is kind of interesting on the history of PostgreSQL

Do you think we've answered Paul's question yet? <g> I supose this isn't going to qualify as a musical thread.

      - Mark