Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/606#discussion_r213189883
--- Diff: src/java/main/org/apache/zookeeper/server/DataTree.java ---
@@ -941,22 +945,41 @@ public ProcessTxnResult processTxn(TxnHeader header,
Record txn)
LOG.debug("Failed: " + header + ":" + txn, e);
}
}
+
+
/*
- * A snapshot might be in progress while we are modifying the data
- * tree. If we set lastProcessedZxid prior to making corresponding
- * change to the tree, then the zxid associated with the snapshot
- * file will be ahead of its contents. Thus, while restoring from
- * the snapshot, the restore method will not apply the transaction
- * for zxid associated with the snapshot file, since the restore
- * method assumes that transaction to be present in the snapshot.
+ * Things we can only update after the whole txn is applied to data
+ * tree.
*
- * To avoid this, we first apply the transaction and then modify
- * lastProcessedZxid. During restore, we correctly handle the
- * case where the snapshot contains data ahead of the zxid
associated
- * with the file.
+ * If we update the lastProcessedZxid with the first sub txn in
multi
+ * and there is a snapshot in progress, it's possible that the zxid
+ * associated with the snapshot only include partial of the multi
op.
+ *
+ * When loading snapshot, it will only load the txns after the zxid
+ * associated with snapshot file, which could data inconsistency
due
--- End diff --
nit: which could **cause** data inconsistency
---
