You manually start a compaction when automated compaction fails for some reason to perform housekeeping of files as needed.
ALTER TABLE tablename [PARTITION (partition_key='partition_value' [,...])] COMPACT 'compaction_type'
Execute a query to start a major compaction of a table.
ALTER TABLE mytable COMPACT 'compaction_type'
ALTER TABLE compacts tables even if the NO_AUTO_COMPACTION table property is set.