Sizing NameNode heap memory
Each workload has a unique byte-distribution profile. Some workloads can use the default JVM settings for heap memory and garbage collection, but others require tuning. You can size your NameNode JVM if the dynamic heap settings cause a bottleneck.
All Hadoop processes run on a Java Virtual Machine (JVM). Each daemon runs on its own JVM across a cluster of hosts.
The legacy NameNode configuration is one active (and primary) NameNode for the entire namespace and one Secondary NameNode for checkpoints (but not failover). The recommended high-availability configuration replaces the Secondary NameNode with a standby NameNode that prevents a single point of failure. Each NameNode uses its own JVM.