Using nodetool sjk

Use nodetool sjk mx to gather database information from MBeans.

Nodetool includes the open source Swiss Java Knife as a built-in command, nodetool sjk, for troubleshooting. This section focuses on using the mx subcommand to get and set JMX MBean values.

Attention: The nodetool sjk mxdump command tries to print all exposed MBeans to the console. The command can fail if it encounters an improperly formatted MBean. To interact with a specific list of MBeans, use the

nodetool sjk
    mx

command.

Listing MBean names

To get values from the command line, first get the complete name of the MBean.

Following is an example of how to use jmxterm to dump the full list of JMX MBeans from a database node:

echo "beans" | java -jar jmxterm-1.0.0-uber.jar -l localhost:7199 -n 2>&1

Tip: Only perform this operation once because the list can be large or search MBeans with particular names in the output by redirecting the result to another filter. For example to find MBeans that contain the word commitlog:

echo "beans" | java -jar /tmp/jmxterm-1.0.0-uber.jar -l localhost:7199 -n 2>&1 | grep -i commitlog

The results provide the exact MBean strings to use in nodetool sjk mx command.

com.datastax.bdp.advrep.v2.metrics:name=CommitLogMessagesRead,type=ReplicationLog
com.datastax.bdp.advrep.v2.metrics:name=CommitLogsDeleted,type=ReplicationLog
com.datastax.bdp.advrep.v2.metrics:name=CommitLogsToConsume,type=ReplicationLog
org.apache.cassandra.db:type=Commitlog
org.apache.cassandra.metrics:name=CompletedTasks,type=CommitLog
org.apache.cassandra.metrics:name=PendingTasks,type=CommitLog
org.apache.cassandra.metrics:name=TotalCommitLogSize,type=CommitLog
org.apache.cassandra.metrics:name=WaitingOnCommit,type=CommitLog
org.apache.cassandra.metrics:name=WaitingOnSegmentAllocation,type=CommitLog

Getting the MBean options and values

Use the MBean information option to show available values. For example, to show the options available for TotalCommitLogSize from the previous results, use the complete name:

nodetool sjk mx -b "org.apache.cassandra.metrics:name=TotalCommitLogSize,type=CommitLog" -mi

org.apache.cassandra.metrics:type=CommitLog,name=TotalCommitLogSize
org.apache.cassandra.metrics.CassandraMetricsRegistry$JmxGauge
 - Information on the management interface of the MBean
 (A) Value : java.lang.Object
  - Attribute exposed for management
 (O) objectName() : javax.management.ObjectName
  - Operation exposed for management

The MBean has a simple value. To read the single number, run the following command:

nodetool sjk mx -b "org.apache.cassandra.metrics:name=TotalCommitLogSize,type=CommitLog" -f Value -mg

org.apache.cassandra.metrics:type=CommitLog,name=TotalCommitLogSize
67108864

Note: SJK is case-sensitive, enter the names exactly.

To check on a more complex metric such as latency, find out how many values are available by using -mi option:

nodetool sjk mx -b "org.apache.cassandra.metrics:name=Latency,scope=Read,type=ClientRequest" -mi

org.apache.cassandra.metrics:type=ClientRequest,scope=Read,name=Latency
org.apache.cassandra.metrics.CassandraMetricsRegistry$JmxTimer
 - Information on the management interface of the MBean
 (A) Max : double
  - Attribute exposed for management
 (A) Min : double
  - Attribute exposed for management
 (A) Mean : double
  - Attribute exposed for management
 (A) StdDev : double
  - Attribute exposed for management
 (A) 95thPercentile : double
  - Attribute exposed for management
 (A) DurationUnit : String
  - Attribute exposed for management
 (A) 50thPercentile : double
  - Attribute exposed for management
 (A) 75thPercentile : double
  - Attribute exposed for management
 (A) 98thPercentile : double
  - Attribute exposed for management
 (A) 99thPercentile : double
  - Attribute exposed for management
 (A) 999thPercentile : double
  - Attribute exposed for management
 (A) OneMinuteRate : double
  - Attribute exposed for management
 (A) FifteenMinuteRate : double
  - Attribute exposed for management
 (A) FiveMinuteRate : double
  - Attribute exposed for management
 (A) MeanRate : double
  - Attribute exposed for management
 (A) RateUnit : String
  - Attribute exposed for management
 (A) Count : long
  - Attribute exposed for management
 (O) values() : long[]
  - Operation exposed for management
 (O) objectName() : javax.management.ObjectName
  - Operation exposed for management

Then to read out a single value from this metric, use the following command:

nodetool sjk mx -b "org.apache.cassandra.metrics:name=Latency,scope=Read,type=ClientRequest" -f 99thPercentile -mg

org.apache.cassandra.metrics:type=ClientRequest,scope=Read,name=Latency
3379.391