问题
How to set Cassandra (>2.0) JVM heap size of 8GB? When I type in free -m it gives me the following. How can I set the Cassandra JVM heap size to 8GB?
total used free shared buffers cached
Mem: 16047 11336 4711 0 81 5814
-/+ buffers/cache: 5441 10606
Swap: 0 0 0
回答1:
As stated in the Tuning Java resources section of the documentation:
If you decide to change the Java heap sizing, both MAX_HEAP_SIZE and HEAP_NEWSIZE should should be set together in conf/cassandra-env.sh.
Inside cassandra-env.sh, search for this line:
#MAX_HEAP_SIZE="4G"
That line in the code happens after the MAX_HEAP_SIZE calculations have happened, so it works as an override. Uncomment it, and set it accordingly.
MAX_HEAP_SIZE="8G"
Be careful going above 8G. For guidance on tuning the JVM, I recommend Amy Tobey's Cassandra 2.1 Tuning Guide. She offers some tips for tuning CMS, as well as a great section on implementing the new G1GC.
回答2:
Update cassandra-env.sh
remove / comment out the entire calculate_heap_sizes() function
- this is the function that is called by cassandra to automatically allocate JVM size.
- it takes the lower of 1/4 system memory or 8GB. This is why the default max JVM size is 8GB
Remove/comment out other line with $MAX_HEAP_SIZE.
The line starts with: "only calcuate the size if..."
delete / keep HEAP_NEWSIZE commented out
set MAX_HEAP_SIZE to the new value. Ex: 16G
- this should be the only place you need to do this
Restart
- Ideally, you'd only need to restart the Cassandra service. However, I've only gotten it to work after restarting the entire machine.
Also see for another example: https://medium.com/@mlowicki/move-cassandra-2-1-to-g1-garbage-collector-b9fb27365509
来源：https://stackoverflow.com/questions/34745419/how-to-set-cassandra-2-0-jvm-heap-size-of-8gb