Table statistics 

Compaction metrics provide a number of statistics that are important for monitoring performance trends.

For individual tables, ColumnFamilyStoreMBean provides the same general latency attributes as StorageProxyMBean. Unlike StorageProxyMBean, ColumnFamilyStoreMBean has a number of other statistics that are important to monitor for performance trends. The most important of these are:
Table Statistics
Attribute Description
MemtableDataSize The total size consumed by this table's data (not including metadata).
MemtableColumnsCount Returns the total number of columns present in the memtable (across all keys).
MemtableSwitchCount How many times the memtable has been flushed out.
RecentReadLatencyMicros The average read latency since the last call to this bean.
RecentWriterLatencyMicros The average write latency since the last call to this bean.
LiveSSTableCount The number of live SSTables for this table.

The recent read latency and write latency counters are important in making sure operations are happening in a consistent manner. If these counters start to increase after a period of staying flat, you probably need to add capacity to the cluster.

You can set a threshold and monitor LiveSSTableCount to ensure that the number of SSTables for a given table does not become too great.