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RocksDB compaction notes

Background work is part of the write path, even when the caller cannot see it.

rocksdblsm-tree

Why compact?

Compaction merges sorted runs and can discard obsolete versions when they are no longer needed. It exchanges background I/O for more manageable read and space costs.

See LSM Tree for the broader write path.

What to measure

  • Bytes written per application byte
  • Pending compaction work
  • Read latency while compaction is active
  • Write stalls under sustained load

Open question

What changes when the storage engine supports a replicated service such as one built around Raft?

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