Before Raft truncates the log, it needs to retrieve a snapshot of the SQLite database to represent the log entries that are removed during that truncation. Raft then writes that snapshot to disk. To reduce both disk IO and disk space this change compresses that SQLite snapshot before it is written to disk, and decompresses it during a restore operation.
This change also deals with older SQLite snapshots, which were not compressed.
Philip O'Toole