Cassandra deletes write tombstones. Tombstones survive until gc_grace_seconds + repair.

What you're seeing

A delete in Cassandra writes a tombstone row marking 'this key is deleted'. Reads must scan all tombstones until they're garbage collected.

gc_grace_seconds (default 10 days) lets repair propagate tombstones to all replicas before they're dropped. Otherwise zombie rows reappear from un-repaired replicas.

★ KEY TAKEAWAY
Cassandra deletes = tombstones. Persist until gc_grace + repair. Read scan cost grows with un-cleared tombstones.
▶ WHAT TO TRY
  • Write 10, delete 5 — see tombstones appear.
  • Run repair, then trigger GC — tombstones drop.
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