CommitLog
Append-only, per-node. Written durably before ack (with commitlog_sync = periodic or batch). On crash, replay CommitLog into MemTable.
Advertisement
MemTable
Per-CF sorted structure in memory. Skiplist/tree of cells. On flush threshold: dump to SSTable, delete CommitLog segment.
Advertisement
SSTable
Sorted String Table. Immutable. Data file + index + summary + Bloom filter + statistics + compression info. Compaction merges + deletes tombstones.