Tombstones in memtable

[Rahul Reddy]

We have small table records are about 5k .
All the inserts comes as 4hr ttl and we have table level ttl 1 day and gc
grace seconds has 3 hours.  We do 5k reads a second during peak load.
During the peak load seeing Alerts for tomstone scanned histogram reaching
million.
Cassandra version 3.11.1. Please let me know how can this tombstone scan
can be avoided in memtable