Tombstones costs disk utilization and increased query time. Monitoring the amount of tomb_stones data is an important part of monitoring the health of a Cassandra cluster. We can use the SSTablemetadata command to get information on a particular table’s tombstone ratio. We can simply clear the tomb_stones data in Cassandra by altering the GC_GRACE_SECONDS

The number of seconds after data is marked with a tombstone (deletion marker) before it is eligible for garbage-collection. Cassandra will not execute hints or batched mutations on a tomb_stones record within its GC_GRACE_SECONDS. The default value allows a great deal of time for Cassandra to maximize consistency prior to deletion. Default value 864000 [10 days]. To learn more about GC_GRACE_SECONDS

Let’s understand how to decreasing GC_GRACE_SECONDS and garbage collection.

Clean tombstones in Cassandra

• Get the GC_GRACE_SECONDS value of the table, store it in some file.

• Alter to reduce the GC_GRACE_SECONDS to 30

  alter table [universe_table] with GC_GRACE_SECONDS = 30;

Wait for 30-60 seconds to cleanup the tombstones and continue to alter to the last value.

• Replace it back with actual value

alter table [universe_table] with GC_GRACE_SECONDS = 86400;

In Cassandra 3.10+

This cleans up all the garbage from whole keyspace or a specific table.

nodetool garbagecollect [jinnabalu_keyspace] [universe_table]

    Question: Can I force cleanup of old tombstones?
    Ans: Yes, you can clean the tomb_stones by decreasing GC_GRACE_SECONDS value to as minimum as possible. and reset back GC_GRACE_SECONDS value to the previous values, once cleaning the tomb_stones.