On Thu, Nov 28, 2013 at 7:21 PM, Robert Wille <rwille@fold3.com> wrote:
So here’s my question. If Cassandra only compacts one table at a time, then I should be safe if I keep as much free space as there is data in the largest table. If Cassandra can compact multiple tables simultaneously, then it seems that I need as much free space as all the tables put together, which means no more than 50% utilization.

If the number of SSTables is [x], then :

- "minor" compaction runs on 1-[x-1] SSTables (in practice, usually a smaller number depending on config)
- "major" compaction runs on [x] SSTables

Unless you run a major compaction manually while using Size Tiered Compaction, you are very unlikely to run a major compaction in normal operation.

Level compaciton strategy has a different set of assumptions.