> 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 

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