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Posted to pr@cassandra.apache.org by "bschoening (via GitHub)" <gi...@apache.org> on 2025/08/02 01:39:18 UTC
[PR] CASSANDRA-20800: Updated tombstone note to clarify behavior with TTL and gc_grace_seconds [cassandra]
bschoening opened a new pull request, #4289:
URL: https://github.com/apache/cassandra/pull/4289
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Re: [PR] CASSANDRA-20800: Updated tombstone note to clarify behavior with TTL and gc_grace_seconds [cassandra]
Posted by "Copilot (via GitHub)" <gi...@apache.org>.
Copilot commented on code in PR #4289:
URL: https://github.com/apache/cassandra/pull/4289#discussion_r2249058635
##########
doc/modules/cassandra/pages/managing/operating/compaction/tombstones.adoc:
##########
@@ -13,8 +13,9 @@ At the end of its expiration period, the grace period, the tombstone is deleted
[NOTE]
====
-You can also mark a {cassandra} row or column with a time-to-live (TTL) value.
-After this amount of time has ended, {cassandra} marks the object with a tombstone, and handles it like other tombstoned objects.
+You can set a Time-To-Live (TTL) value to a row or column. If the data is compacted after the TTL has expired
+but before `gc_grace_seconds` has passed, the data will be written with an expired flag set to True, effectively acting as a tombstone.
+This situation arises only when gc_grace_seconds exceeds the original TTL.
Review Comment:
The documentation should clarify what happens in the more common case when TTL is greater than gc_grace_seconds, or when they are equal, to provide a complete picture of TTL behavior.
```suggestion
- If `gc_grace_seconds` exceeds the original TTL, the expired data (tombstone) will be retained until `gc_grace_seconds` elapses, ensuring that deleted data is not resurrected due to late replica synchronization.
- If the TTL is greater than `gc_grace_seconds`, or if they are equal, the tombstone may be eligible for removal as soon as `gc_grace_seconds` has elapsed, which could result in the data being permanently deleted before all replicas have had a chance to synchronize. This increases the risk of deleted data reappearing (zombies) if a replica was down during the grace period.
For safety, it is generally recommended to set `gc_grace_seconds` to a value greater than or equal to the maximum TTL used in the table, to avoid the risk of zombie data.
```
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Re: [PR] CASSANDRA-20800: Updated tombstone note to clarify behavior with TTL and gc_grace_seconds [cassandra]
Posted by "bschoening (via GitHub)" <gi...@apache.org>.
bschoening closed pull request #4289: CASSANDRA-20800: Updated tombstone note to clarify behavior with TTL and gc_grace_seconds
URL: https://github.com/apache/cassandra/pull/4289
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