Row count of a column family in Cassandra

Question

Is there a way to get a row count (key count) of a single column family in Cassandra? get_count can only be used to get the column count.

For instance, if I have a column family containing users and wanted to get the number of users. How could I do it? Each user is it's own row.

Answer 1

If you are working on a large data set and are okay with a pretty good approximation, I highly recommend using the command:

nodetool --host <hostname> cfstats 

This will dump out a list for each column family looking like this:

Column Family: widgets SSTable count: 11 Space used (live): 4295810363 Space used (total): 4295810363 Number of Keys (estimate): 9709824 Memtable Columns Count: 99008 Memtable Data Size: 150297312 Memtable Switch Count: 434 Read Count: 9716802 Read Latency: 0.036 ms. Write Count: 9716806 Write Latency: 0.024 ms. Pending Tasks: 0 Bloom Filter False Postives: 10428 Bloom Filter False Ratio: 1.00000 Bloom Filter Space Used: 18216448 Compacted row minimum size: 771 Compacted row maximum size: 263210 Compacted row mean size: 1634 

The "Number of Keys (estimate)" row is a good guess across the cluster and the performance is a lot faster than explicit count approaches.