[BTreeNode.write](https://github.com/myui/btree4j/blob/master/src/main/java/btree4j/BTree.java#L1019) and read operation should be atomic for a better Durability (sudden shutdown etc). To do that, undo log is required.
BTreeNode.write and read operation should be atomic for a better Durability (sudden shutdown etc).
To do that, undo log is required.