Deletion in Closed Hash Tables
Simply removing an association can break "chains" formed after collisions and make it difficult to perform GET operations on associations that collided with now-deleted associations.
Therefore, it is common to use a "delete bit" to mark an association as deleted.
When the table gets too full of associations and deleted associations, rehashing is necessary. The rehashing may use a table of the same size as or smaller than before (if many of the entries are deleted entries), or it may use a larger table.