Memtable

A memtable is an in-memory structure that holds recent writes before they are flushed into a persistent sorted table. Readers normally consult it alongside older on-disk components to obtain the current value.

Many engines also record writes in a write-ahead log so a crash does not lose the entire unflushed memtable. Its size and flushing behavior affect memory usage, write bursts, and the amount of compaction work generated.