###########################################################################
#                             jvm.options                                 #
#                                                                         #
# - all flags defined here will be used by cassandra to startup the JVM   #
# - one flag should be specified per line                                 #
# - lines that do not start with '-' will be ignored                      #
# - only static flags are accepted (no variables or parameters)           #
# - dynamic flags will be appended to these on cassandra-env              #
###########################################################################

######################
# STARTUP PARAMETERS #
######################

# Uncomment any of the following properties to enable specific startup parameters

# In a multi-instance deployment, multiple Cassandra instances will independently assume that all
# CPU processors are available to it. This setting allows you to specify a smaller set of processors
# and perhaps have affinity.
#-Dcassandra.available_processors=number_of_processors

# The directory location of the cassandra.yaml file.
#-Dcassandra.config=directory

# Sets the initial partitioner token for a node the first time the node is started.
#-Dcassandra.initial_token=token

# Set to false to start Cassandra on a node but not have the node join the cluster.
#-Dcassandra.join_ring=true|false

# Set to false to clear all gossip state for the node on restart. Use when you have changed node
# information in cassandra.yaml (such as listen_address).
#-Dcassandra.load_ring_state=true|false

# Enable pluggable metrics reporter. See Pluggable metrics reporting in Cassandra 2.0.2.
#-Dcassandra.metricsReporterConfigFile=file

# Set the port on which the CQL native transport listens for clients. (Default: 9042)
#-Dcassandra.native_transport_port=port

# Overrides the partitioner. (Default: org.apache.cassandra.dht.Murmur3Partitioner)
#-Dcassandra.partitioner=partitioner

# To replace a node that has died, restart a new node in its place specifying the address of the
# dead node. The new node must not have any data in its data directory, that is, it must be in the
# same state as before bootstrapping.
#-Dcassandra.replace_address=listen_address or broadcast_address of dead node

# Allow restoring specific tables from an archived commit log.
#-Dcassandra.replayList=table

# Allows overriding of the default RING_DELAY (1000ms), which is the amount of time a node waits
# before joining the ring.
#-Dcassandra.ring_delay_ms=ms

# Set the port for the Thrift RPC service, which is used for client connections. (Default: 9160)
#-Dcassandra.rpc_port=port

# Set the SSL port for encrypted communication. (Default: 7001)
#-Dcassandra.ssl_storage_port=port

# Enable or disable the native transport server. See start_native_transport in cassandra.yaml.
# cassandra.start_native_transport=true|false

# Enable or disable the Thrift RPC server. (Default: true)
#-Dcassandra.start_rpc=true/false

# Set the port for inter-node communication. (Default: 7000)
#-Dcassandra.storage_port=port

# Set the default location for the trigger JARs. (Default: conf/triggers)
#-Dcassandra.triggers_dir=directory

# For testing new compaction and compression strategies. It allows you to experiment with different
# strategies and benchmark write performance differences without affecting the production workload. 
#-Dcassandra.write_survey=true

# To disable configuration via JMX of auth caches (such as those for credentials, permissions and
# roles). This will mean those config options can only be set (persistently) in cassandra.yaml
# and will require a restart for new values to take effect.
#-Dcassandra.disable_auth_caches_remote_configuration=true

########################
# GENERAL JVM SETTINGS #
########################

# enable assertions.  disabling this in production will give a modest
# performance benefit (around 5%).
-ea

# enable thread priorities, primarily so we can give periodic tasks
# a lower priority to avoid interfering with client workload
-XX:+UseThreadPriorities

# allows lowering thread priority without being root on linux - probably
# not necessary on Windows but doesn't harm anything.
# see http://tech.stolsvik.com/2010/01/linux-java-thread-priorities-workar
-XX:ThreadPriorityPolicy=42

# Enable heap-dump if there's an OOM
-XX:+HeapDumpOnOutOfMemoryError

# Per-thread stack size.
-Xss256k

# Larger interned string table, for gossip's benefit (CASSANDRA-6410)
-XX:StringTableSize=1000003

# Make sure all memory is faulted and zeroed on startup.
# This helps prevent soft faults in containers and makes
# transparent hugepage allocation more effective.
-XX:+AlwaysPreTouch

# Disable biased locking as it does not benefit Cassandra.
-XX:-UseBiasedLocking

# Enable thread-local allocation blocks and allow the JVM to automatically
# resize them at runtime.
-XX:+UseTLAB
-XX:+ResizeTLAB

# http://www.evanjones.ca/jvm-mmap-pause.html
-XX:+PerfDisableSharedMem

# Prefer binding to IPv4 network intefaces (when net.ipv6.bindv6only=1). See
# http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6342561 (short version:
# comment out this entry to enable IPv6 support).
-Djava.net.preferIPv4Stack=true

### Debug options

# uncomment to enable flight recorder
#-XX:+UnlockCommercialFeatures
#-XX:+FlightRecorder

# uncomment to have Cassandra JVM listen for remote debuggers/profilers on port 1414
#-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=1414

# uncomment to have Cassandra JVM log internal method compilation (developers only)
#-XX:+UnlockDiagnosticVMOptions
#-XX:+LogCompilation

#################
# HEAP SETTINGS #
#################

# Heap size is automatically calculated by cassandra-env based on this
# formula: max(min(1/2 ram, 1024MB), min(1/4 ram, 8GB))
# That is:
# - calculate 1/2 ram and cap to 1024MB
# - calculate 1/4 ram and cap to 8192MB
# - pick the max
#
# For production use you may wish to adjust this for your environment.
# If that's the case, uncomment the -Xmx and Xms options below to override the
# automatic calculation of JVM heap memory.
#
# It is recommended to set min (-Xms) and max (-Xmx) heap sizes to
# the same value to avoid stop-the-world GC pauses during resize, and
# so that we can lock the heap in memory on startup to prevent any
# of it from being swapped out.
#-Xms4G
#-Xmx4G

# Young generation size is automatically calculated by cassandra-env
# based on this formula: min(100 * num_cores, 1/4 * heap size)
#
# The main trade-off for the young generation is that the larger it
# is, the longer GC pause times will be. The shorter it is, the more
# expensive GC will be (usually).
#
# It is not recommended to set the young generation size if using the
# G1 GC, since that will override the target pause-time goal.
# More info: http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html
#
# The example below assumes a modern 8-core+ machine for decent
# times. If in doubt, and if you do not particularly want to tweak, go
# 100 MB per physical CPU core.
#-Xmn800M

#################
#  GC SETTINGS  #
#################

### CMS Settings

-XX:+UseParNewGC
-XX:+UseConcMarkSweepGC
-XX:+CMSParallelRemarkEnabled
-XX:SurvivorRatio=8
-XX:MaxTenuringThreshold=1
-XX:CMSInitiatingOccupancyFraction=75
-XX:+UseCMSInitiatingOccupancyOnly
-XX:CMSWaitDuration=10000
-XX:+CMSParallelInitialMarkEnabled
-XX:+CMSEdenChunksRecordAlways
# some JVMs will fill up their heap when accessed via JMX, see CASSANDRA-6541
-XX:+CMSClassUnloadingEnabled

### G1 Settings (experimental, comment previous section and uncomment section below to enable)

## Use the Hotspot garbage-first collector.
#-XX:+UseG1GC
#
## Have the JVM do less remembered set work during STW, instead
## preferring concurrent GC. Reduces p99.9 latency.
#-XX:G1RSetUpdatingPauseTimePercent=5
#
## Main G1GC tunable: lowering the pause target will lower throughput and vise versa.
## 200ms is the JVM default and lowest viable setting
## 1000ms increases throughput. Keep it smaller than the timeouts in cassandra.yaml.
#-XX:MaxGCPauseMillis=500

## Optional G1 Settings

# Save CPU time on large (>= 16GB) heaps by delaying region scanning
# until the heap is 70% full. The default in Hotspot 8u40 is 40%.
#-XX:InitiatingHeapOccupancyPercent=70

# For systems with > 8 cores, the default ParallelGCThreads is 5/8 the number of logical cores.
# Otherwise equal to the number of cores when 8 or less.
# Machines with > 10 cores should try setting these to <= full cores.
#-XX:ParallelGCThreads=16
# By default, ConcGCThreads is 1/4 of ParallelGCThreads.
# Setting both to the same value can reduce STW durations.
#-XX:ConcGCThreads=16

### GC logging options -- uncomment to enable

-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintHeapAtGC
-XX:+PrintTenuringDistribution
-XX:+PrintGCApplicationStoppedTime
-XX:+PrintPromotionFailure
#-XX:PrintFLSStatistics=1
#-Xloggc:/var/log/cassandra/gc.log
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=10
-XX:GCLogFileSize=10M