I¹m trying to estimate our disk space requirements and I¹m wondering about disk space required for compaction.
My application mostly inserts new data and performs updates to existing data very infrequently, so there will be very few bytes removed by compaction. It seems that if a major compaction occurs, that performing the compaction will require as much disk space as is currently consumed by the table. So here¹s 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. So, how much free space do I need? Any rules of thumb anyone can offer? Also, what happens if a node gets low on disk space and there isn¹t enough available for compaction? If I add new nodes to reduce the amount of data on each node, I assume the space won¹t be reclaimed until a compaction event occurs. Is there a way to salvage a node that gets into a state where it cannot compact its tables? Thanks Robert
