Auto Compaction Tips

The auto compaction is a stateful process. It means, druid stores the last compaction state in every segment you have. When auto compaction searches for segments to compact, it checks whether or not the last compaction state matches to the current compaction config. If they match, auto compaction skips those segments no matter how they are sized/partitioned. You can see the last compaction state in the “Segments” tab by clicking the details button.
or you can run the below query

select last_compaction_state from sys.segments where datasource = 'your_datasource'

If you want to trigger the compaction for those segments again, you need to update the compaction config to not match to the last compaction state.