Using the nodetool Utility

The nodetool utility is a command-line interface for managing a cluster.

• A command-line interface for monitoring Cassandra
• Also used for performing routine database operations
• Run directly from an operating Cassandra node

Note: If the node from which you issue the command is the intended target, you do not need the -h option to identify the target; otherwise, for remote invocation, identify the target node, or nodes, using -h.

How does it work?:

• JMX(Java Management Extention) command line wrapper.
• Communicates with JMX to perform Operation and Monitoring tasks exposed by MBeans
• JMX is a Java technology that supplies tools for managing and monitoring Java applications and services.

Where does it work on? :

The nodetool commands can be categorized into these groups: 1) Cluster 2) Server 3) Backup 4) Storage 5) Compaction 6) Network


nodetool status:

Type of commands: Cluster

• This has to do with working with the cluster-wide information
• As the point-of-view of that node as it sees the state of the cluster.

1) nodetool status

• Provides information about the cluster, such as the state, load, and IDs.
• Who's up and who's down.
• This is probably the most used nodetool command.

$ nodetool <options> status <keyspace>

2) nodetool repair

• Starts a repair process from the point of the view of that node.
• Repairs one or more keyspaces, tables.

$ nodetool <options> repair

Type of commands: Node

• Scope of the commands are at the node level.

1) nodetool info

• Provides node information such as load and uptime
• Status of the JVM
• Use the "T" flag to display all tokens

$ nodetool <options> info ( -T | --tokens )

2) nodetool tpstats

• Provides usage statistics of thread pools
• How many completed, how many pending, which ones are blocked.
• A high number of pending tasks for any pool can indicate performance problems
• Shows mutation drops( critical for troubleshooting a node)
• A heavily used command during troubleshooting

$ nodetool <options> tpstats

Statuses: Active, Pending, Completed, Blocked, All time blocked, Pool Names : ReadStage RequestReleaseStage MutationStage ReadRepairStage GossipStage Anti-EntropyStage MigrationStage MemoryMeter MemtablePostFlusher FlushWriter Commitlog_Archiver InternalResponseStage HintedHandoff Message Type: Type of operations get dropped Range_Slice Read_Repair Paged_Range Binary Read Mutation _Trace Request_Response Counter_Mutation
3) nodetool tablehistograms

• The nodetool tablehistograms command provides statistics about a table
• Includes read/write latency, partition size, column count, and number of SSTABLES
• The report is incremental, not cumulative.
• It covers all the operation since the last time nodetool tablehistograms was run in the current session.
• The use of the metrics-core library makes the output more informative and easier to understand
• These statistics could be used to plot a frequency function.

$ nodetool <options> tablehistograms -- <keyspace>.<table>

Type of commands: Backup

1) nodetool snapshot

• We can take a snapshot of one or more keyspaces, or of a table, to backup data.
• Cassandra flushes the node before taking the snapshot.
• Takes the snapshot and store the data in the snapshot directory of each keyspace in the data directory.
• If you do not specify the name of the snapshot directory using the -T option, Cassandra names the directory using the timestamp of the snapshot like 398276394348934.

$ nodetool <options> snapshot Example: Snapshot all keyspaces $ nodetool snapshot Example: Snapshot single keypsace $ nodetool snapshot -t 2016.05.17 killrvideo Example: Multiple keyspace snapshot $ nodetool snapshot mykeyspace killrvideo Example: Single table snapshot $ nodetool snapshot --table users killrvideo Example: Snapshot different tables from different keyspaces $ nodetool snapshot -kt Cycling.Cyclist_Name, KillrVideo.Users

2) nodetool clearsnapshot:

• Removes one or more snapshots.

$ nodetool <options> clearsnapshot --t snapshot --keyspace Keyspace_Name

3) nodetool listsnapshots:

• Lists snapshot names, size on disk, and true size.

  $ nodetool <options> listsnapshots

Type of commands: Storage
1) nodetool cleanup:

• Used to get rid of old data on nodes after bootstrap operations.

$ nodetool <options> cleanup -- <keyspace> (<table> ...)

2) nodetool flush:

• The command flushes everything in the memtables out to SSTables and deletes all commitlog segments.
• You can specify a keyspace followed by one or more tables that you want to flush from the memtable to SSTables on disk.

$ nodetool <options> flush -- <keyspace> ( <table> ... )

Type of commands: Compaction 1) nodetool compact:

• Forces a major compaction on one or more tables for size tired compaction.
• Acts differently for different compaction strategies.

$ nodetool <options> compact <keyspace> (<table> ...)

2) nodetool compactionstats:

• Provides statistics about a compaction
• Not something you would just run all the time.
• This is a JMX statistic you could also pull in using OpsCenter
• See what is currently compacting

$ nodetool <options> compactionstats -H

* H converts bytes to human-readable form: KB, MB, GB, or TB

Type of commands: Network

1) nodetool proxyhistograms:

• Provides a histogram of network statistics
• The output of this command shows the full request latency recorded by the coordinator.
• Includes the percentile rank of the read and write latency values for inter-node communication
• Typically, you use the command to see if requests encounter a slow node.

       $ nodetool <options> proxyhistograms

2) nodetool netstats:

• Provides network information about host
• The default host is the connect host if the user does not include a hostname or ip-address in the command.

$ nodetool <options> netstats -H