Java reports an error saying there are too many open files in Apache Cassandra 

Java may not have enough open file descriptors on Linux platforms.

Attention: DataStax Enterprise customers. Do not use the topics in this section. See Troubleshooting DataStax Enterprise.

Java may not have enough open file descriptors on Linux platforms.

Cassandra generally needs more than the default (1024) amount of file descriptors. To increase the number of file descriptors, change the security limits on your Cassandra nodes as described in the Recommended Settings section of Insufficient user resource limits errors.

Another, much less likely possibility, is a file descriptor leak in Cassandra. Run lsof -n | grep java to check that the number of file descriptors opened by Java is reasonable and report the error if the number is greater than a few thousand.