Slow Cassandra database performance

The following warning:

Unable to lock JVM memory (ENOMEM). This can result in part of the JVM being swapped out, especially with mmapped I/O enabled

encountered in the cassandra-stderr.log file indicates insufficient memory lock settings. Even though most of the time it will not cause any problem, it may potentially affect Cassandra performance in some cases.

Solution

Increase memory lock limit by running the ulimit command, or, if you work in Debian, modify the /etc/security/limits.conf file — change max locked memory to unlimited for the user under which Cassandra runs.