By default, the Primary key, Display Key (and all columns that make up the display key) are saved. So I'll assume you included those when you say 5 saved columns.

Tombstones on Cassandra side are created in the following cases:

• DELETE command
• Expired data (TTL)
• INSERT or UPDATE command with a null value
• Inserting data into parts of a collection

1. When deleting a row with 5 saved columns (e.g. PK and 4 other columns that have save option) you will create 5 tombstones (on row level in Cassandra as every saved table cell is a row in the elementdata table in Cassandra)
2. This one I'm not a 100% sure and I would need to verify with SW, but if we write a null towards the table cells in Cassandra we potentially have 2 tombstones for every clear on a cell/parameter (on cell level in Cassandra on two columns v and vu)
3. This should not result in a tombstone on the elementdata table
4. It all depends what DataMiner will send towards the DB layer when doing certain commands (e.g. fillarray, setparameters, ...). If you want to verify how your tombstones increase you can connect with CQLSH on the linux machine and run the command 'select * from "SLDMADB".elementdata where d = 514 and e = 115;' with tracing enabled for your element. This will give you a good understanding how many tombstones are retrieved (see screenshot).

Ref: Managing Tombstones in Apache Cassandra I Instaclustr