Offline compaction/merging of multiple SSTables into one

["Alexander Shukaev (BLOOMBERG/ FRANKFURT)" <as...@bloomberg.net>]

Hi Everyone,

I have the following question [1]:

```
$ cd /tmp
$ cp -r /var/lib/cassandra/data/keyspace/table-6e9e81a0808811e9ace14f79cedcfbc4 .
$ nodetool compact --user-defined table-6e9e81a0808811e9ace14f79cedcfbc4/*-Data.db
```

I expected the two SSTables (where the second one contains only tombstones) to be merged into one, which would be equivalent to the first one minus data masked by tombstones from the second one.

However, the last command returns `0` exit status and nothing changes in the `table-6e9e81a0808811e9ace14f79cedcfbc4` directory (still two tables are there).  Any ideas how to unconditionally merge potentially multiple SSTables into one in the offline manner (like above, not on SSTable files currently used by the running cluster)?

References
----------

[1] https://stackoverflow.com/q/56427498/1743860

Regards,
Alexander