memtable · shipping · also in-memory write buffer (LSM)

Memtable

A memtable is an in-memory structure that holds recent LSM-tree updates before they are flushed to sorted table files.

RocksDB's FAST 2021 architecture description separates the memtable from its recovery WAL and persistent SST files. A memtable flush and an SST compaction are different operations. [1] Do not infer a power-loss guarantee from the in-memory structure's name; the logging and acknowledgment policy must also be specified.

Relations

related

lsm-tree, sstable, compaction, write-ahead-log, rocksdb-column-family

Citations

1. Siying Dong, Andrew Kryczka, Yanqin Jin and Michael Stumm. Evolution of Development Priorities in Key-value Stores Serving Large-scale Applications: The RocksDB Experience. FAST 2021, pp. 33-49; sections 2.2 and 4. (accessed 2026-10-14)
2. RocksDB: a WAL sync is not a memtable flush (accessed 2026-10-14)

JSON: /data/terms/memtable.json