Thread pool and read/write latency statistics

Increases in pending tasks on thread pool statistics can indicate when to add additional capacity.

Cassandra maintains distinct thread pools for different stages of execution. Each of the thread pools provide statistics on the number of tasks that are active, pending, and completed. Trends on these pools for increases in the pending tasks column indicate when to add additional capacity. After a baseline is established, configure alarms for any increases above normal in the pending tasks column. Use nodetool tpstats on the command line to view the thread pool details shown in the following table.
Table 1. Compaction Metrics
Thread Pool Description
AE_SERVICE_STAGE Shows anti-entropy tasks.
CONSISTENCY-MANAGER Handles the background consistency checks if they were triggered from the client's consistency level.
FLUSH-SORTER-POOL Sorts flushes that have been submitted.
FLUSH-WRITER-POOL Writes the sorted flushes.
GOSSIP_STAGE Activity of the Gossip protocol on the ring.
LB-OPERATIONS The number of load balancing operations.
LB-TARGET Used by nodes leaving the ring.
MEMTABLE-POST-FLUSHER Memtable flushes that are waiting to be written to the commit log.
MESSAGE-STREAMING-POOL Streaming operations. Usually triggered by bootstrapping or decommissioning nodes.
MIGRATION_STAGE Tasks resulting from the call of system_* methods in the API that have modified the schema.
MUTATION_STAGE API calls that are modifying data.
READ_STAGE API calls that have read data.
RESPONSE_STAGE Response tasks from other nodes to message streaming from this node.
STREAM_STAGE Stream tasks from this node.

Read/Write latency metrics

Cassandra tracks latency (averages and totals) of read, write, and slicing operations at the server level through StorageProxyMBean.