Must I use for any web application Postgres or Oracle XE and why?

Both are readily available for free as well as for use in a commercial sense.

Why must I personally use one database within the other?

Well, with Oracle XE, should you hit the limits, you need to either buy Oracle or migrate your whole application to another database. With PostgreSQL, you will find no limits, and also the software programs are totally free and open-source.

A couple of things to understand when you purchase Oracle XE:

  1. It'll just use one CPU for those who have a multiprocessor server
  2. It'll just use up to and including more 1 gigabyte of memory
  3. It features a database size limit of four gb for user data
  4. Only accessible for 32-bit Home windows and 32-bit Linux

If individuals restrictions aren't an problem for only you such as the Oracle approach then try it out, otherwise consider an opensource server like Postgres or MySQL, that have no aforementioned restrictions.

Should you choose choose XE after which later find your needs have transformed, the following version from Oracle is 900USD for five seats, as well as an additional 180 per chair. This is actually a little less expensive than MS SQL Server afaik.

You will find some top reasons to choose Oracle, especially if you are a Java developer e.g. you are able to write saved methods in Java, and i believe there's native support for Java web services. Ultimately however you have to consider the price using the needs of the application. MySQL and Postgres will help you to scale the application with no cost (apart from hardware clearly).

when selecting a db vendor make sure match the requirements of the application from the talents from the vendors' db product. And be careful for his or her weak points.

For instance, knowing your creates is going to be as frequent as the reads and both will occur concurrently, then you will want to understand how each vendor you think about handles concurency. Suppliers that depend on elaborate lock managers with complex lock escalation schemes will probably provide you with grief should you expect heavy strain on you application. You'll take more time attempting to deal with the DB's lock manager than really fixing your problems.

That's an example. Every DB has its own talents and weak points to think about. Seek information, look for a site that compares suppliers making a choice that balances your requirements against that. If you're able to have an eval copy, all of the easier to run some evidence of concept tests against. Write scripts that pummel the db in certain much like that which you expect your application to create and move from there. While your in internet marketing, obtain the query plans for that SQL inside your scripts from each vendor and find out what you could study from that about how exactly each vendor's optimizer works.

There's more that may be stated, but hopefully you receive the gist.

What's your platform of preference? Whether it's Home windows, I'd opt for Oracle or MySQL when i often hear only bad reasons for running PostgreSQL on Home windows machines.

Also, Oracle includes a more GUI apprach to configuration therefore if you are not really a Linux hacker, you might enjoy it better.

Postgres however includes a way superior SQL console and console tools generally tend to be more developed and simpler to make use of. Oracle has more tools however the decent ares (like PL/SQL navigator) have a price and also the free ones simply suck.

Keep in mind that selecting a database is really a lengthy-term decision so think about the possible alterations in needs for the application too. If you're not ready to eventually put money into Oracle, better opt for Postgres -- safe option. And adequate for many projects.

You have not provided many details, but unless of course you are already an Oracle expert, I see pointless to select Oracle XE over PostgreSQL. PostgreSQL will be free and is much more capable and much more scalable.

And you will decide to run PostgreSQL on Home windows, Mac OS X or Linux. I believe Oracle XE is restricted to Home windows and Linux.