Memtable
MemTable is an in-memory data structure holding data before they are flushed to SST files. It serves both read and write – new writes always insert data to memtable, and reads has to query memtable before reading from SST files, because data in memtable is newer. Once a memtable is full, it becomes immutable and replaced by a new memtable. A background thread will flush the content of the memtable into a SST file, after which the memtable can be destroyed.
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