How to get tombstone count for a cql query? - cassandra

Question

I am trying to evaluate number of tombstones getting created in one of tables in our application. For that I am trying to use nodetool cfstats. Here is how I am doing it:
create table demo.test(a int, b int, c int, primary key (a));
insert into demo.test(a, b, c) values(1,2,3);
Now I am making the same insert as above. So I expect 3 tombstones to be created. But on running cfstats for this columnfamily, I still see that there are no tombstones created.
nodetool cfstats demo.test
Average live cells per slice (last five minutes): 0.0
Average tombstones per slice (last five minutes): 0.0
Now I tried deleting the record, but still I don't see any tombstones getting created. Is there any thing that I am missing here? Please suggest.
BTW a few other details,
* We are using version 2.1.1 of the Java driver
* We are running against Cassandra 2.1.0

Answer 1

For tombstone counts on a query your best bet is to enable tracing. This will give you the in depth history of a query including how many tombstones had to be read to complete it. This won't give you the total tombstone count, but is most likely more relevant for performance tuning.
In cqlsh you can enable this with
cqlsh> tracing on;
Now tracing requests.
cqlsh> SELECT * FROM ascii_ks.ascii_cs where pkey = 'One';
pkey | ckey1 | data1
------+-------+-------
One | One | One
(1 rows)
Tracing session: 2569d580-719b-11e4-9dd6-557d7f833b69
activity | timestamp | source | source_elapsed
--------------------------------------------------------------------------+--------------+-----------+----------------
execute_cql3_query | 08:26:28,953 | 127.0.0.1 | 0
Parsing SELECT * FROM ascii_ks.ascii_cs where pkey = 'One' LIMIT 10000; | 08:26:28,956 | 127.0.0.1 | 2635
Preparing statement | 08:26:28,960 | 127.0.0.1 | 6951
Executing single-partition query on ascii_cs | 08:26:28,962 | 127.0.0.1 | 9097
Acquiring sstable references | 08:26:28,963 | 127.0.0.1 | 10576
Merging memtable contents | 08:26:28,963 | 127.0.0.1 | 10618
Merging data from sstable 1 | 08:26:28,965 | 127.0.0.1 | 12146
Key cache hit for sstable 1 | 08:26:28,965 | 127.0.0.1 | 12257
Collating all results | 08:26:28,965 | 127.0.0.1 | 12402
Request complete | 08:26:28,965 | 127.0.0.1 | 12638
http://www.datastax.com/dev/blog/tracing-in-cassandra-1-2