Tombstone
A marker that records a deletion in a log-structured store, since you cannot erase in place — later removed by compaction.
A tombstone is a marker written to record that a key was deleted in a log-structured (append-only) store. Because these systems never modify data in place, a delete is actually a new write that says “this key is gone,” and reads that find a tombstone treat the key as absent.
Worked example: deleting a row in Cassandra writes a tombstone; a later read sees the tombstone (newer than the old value) and returns nothing, and eventually compaction drops both the tombstone and the old data. Gotcha: tombstones must live long enough to propagate to every replica (or a deleted row can resurrect from a replica that missed the delete), so they linger — and a table with many deletes accumulates tombstones that slow reads until compaction clears them, a classic Cassandra performance trap.