System Administration - eXist: A NoSQL Database and Application Development Platform - page 389

Figure 15-2. Examining eXist's cache utilization using JConsole
Memory and Cache Tuning
The total memory available to eXist is set through the Java JVM's -Xmx setting. This
setting determines the maximum heap size available to a Java application when a
JVM is started. If a Java application attempts to use more memory than is available, it
receives the dreaded OutOfMemoryError from the JVM. While an application may not
crash immediately, it is more than likely impossible to continue running successfully
after receiving an OutOfMemoryError !
In eXist, all memory is allocated on the heap, so it is important to ensure that you
have enough memory allocated for your database. It is very difficult for us to guide
you in establishing the best -Xmx setting, as every dataset and query workload is dif‐
ferent. If you used the eXist installer, then you will have configured the maximum
memory available to eXist during installation (see “Things to Decide Before Instal‐
ling” on page 20 ). If you did not use the installer, the -Xmx setting will be present in
the script that you use to start up eXist.