Hello, In the process of upgrading our cluster from 2.1 to 2.2 we have triggered the SSTable rewriting process like this:
$ nodetool upgradesstables -j 4 # concurrent_compactors=5 Then if we would immediately check the compactionstats, we see that 4 compactions of type 'Upgrade sstables' are running for the same keyspace/table. Fine. What is surprising, though, is that when any of the tasks which are smaller in size complete, no new tasks are added and we are left waiting for a smaller number of long running tasks to complete, e.g: pending tasks: 4 id compaction type keyspace table completed total unit progress d535e962-00de-11e8-9c2c-ade7b0b922e3 Upgrade sstables cel_data event_history_unbounded 32.87 GB 84.12 GB bytes 39.08% d535e960-00de-11e8-9c2c-ade7b0b922e3 Upgrade sstables cel_data event_history_unbounded 33.15 GB 84.79 GB bytes 39.09% Periodically, an ordinary compaction would be listed, but no new Upgrade tasks appear. Only after all of the "current" tasks are finished, the new 4 tasks are scheduled and the process repeats. We would expect that new tasks would be scheduled as soon as a compaction slot is freed up, but this doesn't seem to happen. Is this by design? I do not see any open issue about this in Jira. Cheers, -- Oleksandr "Alex" Shulgin | Database Engineer | Zalando SE | Tel: +49 176 127-59-707