> by reading the documentation about TTL > https://cassandra.apache.org/doc/4.1/cassandra/operating/compaction/index.html#ttl > It mention that it creates a tombstone when data expired, how does it > possible without writing to the tombstone on the table ? I thought TTL > doesn't create tombstones since the ttl is present together with the write > time timestmap > at the row level
If you read carefully, you will notice that no tombstone is created and instead the data is *converted* into a tombstone. So, after the TTL has expired, the inserted data effectively acts as a tombstone. This is needed, because the now expired data might hide older data that has not expired yet. If the newer data was simply dropped after the TTL expired, older data might reappear. If I understand it correctly, you can avoid data with a TTL being converted into a tombstone by choosing a TTL that is greater than gc_grace_seconds. Technically, the data is still going to be converted into a tombstone when the TTL expires, but this tombstone will immediately be eligible for garbage collection.
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