In an eventual consistent system like Cassandra, information about deleted keys should be stored to avoid reading the deleted data. When a row or column is deleted, this information is stored as tombstone. Tombstones are stored until gc grace period associated with column family not reached. Only major compaction removes tombstones that are older than gc grace period. Tombstones are spread to all replicas when repair is performed. It is important to run repair regularly to eliminate resurre...
