Monitoring - Practical Cassandra - page 115

Memory
The Memory tab consists of graphs about the current state of the memory (see Fig-
ure 8.2 ) . One of the most important memory stats that you want to be aware of is
your current heap usage. It is also the default graph that comes up on the Memory
tab. As with everything else in your system, it is helpful to know what a good
baseline is for heap usage during normal system operations. If you have a 10GB
heap set and you find during most of your operations that you are using only 3GB,
you can likely reduce your JVM maximum heap size. This will enable you to re-
duce your memory footprint on the system and possibly even speed up your GCs.