David, I apologize I did not mention those things explicitly. All the places where sstable files are accessed directly would have to be refactored.
Regarding TableMetrics - currently it includes many metrics, some of them are unrelated to sstables at all, but there are metrics which are specific to the current sstable format, like metrics related to index summaries or bloom filters. The created gauges query certain methods on sstable reader - I think the only common metrics for sstables we can leave in TableMetrics are those for which there are query methods in generic sstable interface. Other metrics, specific to the certain sstable format should be registered by the implementation itself. Speaking about the implementation, one idea I was thinking about was that the factories for formats are registered using Java's native service loader. This way we could get the list of all the factories on the classpath and call some method, like `registerMetrics` during system initialization. That could be also implemented in static initializer in the factory but it would make it less obvious for the implementors where such initialization should be done. I hope this explains a bit Thanks, Jacek
