fix: propagate WAL CRC chain across snapshot recovery#901
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mattisonchao merged 1 commit intomainfrom Feb 24, 2026
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When a follower installs a snapshot, wal.Clear() resets the CRC chain to 0. Since CRC(n) = CRC32(CRC(n-1) + payload(n)), all subsequent WAL CRCs diverge from the leader even though the DB data is identical. Fix this by propagating the previous entry's CRC through the replication protocol. The leader includes previousEntryCrc in every Append message (read from the WAL record), and the follower uses it to seed the CRC chain via AppendAsyncWithPreviousCrc when the WAL is empty after snapshot install. Closes #898 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Motivation
When a follower installs a snapshot,
wal.Clear()resets the CRC chain to 0. SinceCRC(n) = CRC32(CRC(n-1) + payload(n)), all subsequent WAL CRCs diverge from the leader even though the DB data is identical (fixes #898).Modification
previous_entry_crcfield to theAppendprotobuf message for CRC propagation during replication.previousCrcthrough the WAL read chain (ReadRecordWithValidation→segment.Read→wal.readAtIndex→Reader.ReadNext) so the leader can include it in everyAppendmessage.AppendAsyncWithPreviousCrc(entry, previousCrc)to theWalinterface so the follower can seed the CRC chain when appending after snapshot install.readWriteSegmentwhenRecoverIndexreturns an empty segment.U32Zeroconstant tocommon/constantfor typed zero CRC values.TestReadNextReturnsCrcandTestAppendAsyncWithPreviousCrcWAL tests.TestFollowerCursor_SendSnapshotto verify non-zeroPreviousEntryCrcafter snapshot.