Compaction

Compaction rewrites stored data to consolidate overlapping structures and reclaim space occupied by obsolete versions or eligible deletion markers. In an LSM engine, it can also reduce the number of files that a read must inspect.

The work consumes CPU, storage bandwidth, and temporary disk space, so an overloaded compaction process can affect foreground requests. Compaction policy determines how aggressively the engine trades background write work for read efficiency.