I was trying to make a choice today between selecting MySQL and Oracle XE for a BI project. I didn’t know the limitations off-hand and was surprised I had to start digging through Oracle docs to find it. Here they are for your convenience:

CPU Limitations

If Oracle Database XE Server is installed on a computer with more than one CPU (including dual-core CPUs), then it will consume, at most, processing resources equivalent to one CPU. For example, on a computer with two CPUs, if two Oracle database clients try to simultaneously execute CPU-intensive queries, then Oracle Database 10g Standard Edition, Oracle Database 10g Standard Edition One, or Oracle Database 10g Enterprise Edition will use both CPUs to efficiently process the queries. However, with Oracle Database XE Server, the Oracle database will process the queries at the rate of a single CPU even if concurrent processing on two CPUs would be faster. To use the full processing resources of your computer, upgrade to Oracle Database 10g Standard Edition, Oracle Database 10g Standard Edition One, or Oracle Database 10g Enterprise Ed

Data/Space Limitations

The maximum amount of user data in an Oracle Database XE Server database cannot exceed 4 gigabytes. If the user data grows beyond this limit, then an ORA-12592 error will appear. To use more than 4 gigabytes of user data, upgrade to Oracle Database 10g Standard Edition, Oracle Database 10g Standard Edition One, or Oracle Database 10g Enterprise Edition.

RAM Limitations

The maximum amount of RAM that an Oracle Database XE Server database uses cannot exceed 1 gigabyte, even if more is available. Table 1, “Oracle Database XE Requirements” provides the minimum and recommended RAM that you should use. The exact amount of RAM that Oracle Database XE uses is the sum of the System Global Area (SGA) and the aggregate Program Global Area (PGA). To find this value, follow these steps after you have installed Oracle Database XE:

1. Click the Main menu (on Gnome) or the K menu (on KDE), select Oracle Database 10g Express Edition, and then select Go to Database Home Page.
2. In the Database Home Page, log in as SYSTEM.
3. Under Usage Monitor, click the Memory link.
4. Check the Current Configuration (SGA + PGA) setting

Installation Limitations

On a single computer, only one installation of the Oracle Database XE software can be performed. This does not affect any existing installation or new installations of Oracle Database 10g Standard Edition, Oracle Database 10g Standard Edition One, or Oracle Database 10g Enterprise Edition. In addition, users can run only one instance of the Oracle Database XE database on each individual computer. To run more than one Oracle Database server instance or install more than one copy of the database software, upgrade to Oracle Database 10g Standard Edition, Oracle Database 10g Standard Edition One, or Oracle Database 10g Enterprise Edition.

HTTPS Limitations

HTTPS is not supported natively with the HTTP listener built into Oracle Database XE. If you want HTTPS support, use an alternative Web listener, such as Apache, that does provide HTTPS support, and provide proxies for the URLs provided by Oracle Database XE.

Given that this project has a fair amount of data and we want to actually use our hardware (more than 1 CPU and more than 1 GB RAM), we picked MySQL.