.

go/zodb/btree/btree.go

@@ -11,12 +11,26 @@
 //
 // A B⁺ tree consists of nodes. Only leaf tree nodes point to data.
 // Intermediate tree nodes contains keys and pointer to next-level tree nodes.
-// B⁺ tree always have uniform height - that is the path to any leaf node from
-// the tree root is the same.	XXX
 //
-// BTree.Get(key) performs point-query.
+// A well-balanced B⁺ tree always have uniform depth - that is the path to any
+// leaf node from the tree root is the same. However historically ZODB/py does
+// not always balance B⁺ trees well(*), so this property is not preserved.
+// Nevertheless an intermediate B⁺ tree node always has children of the same
+// kind: they are either all leafs or all intermediate nodes(+).
 //
-// B⁺ Trees
+// BTree and Bucket represent an intermediate and a leaf tree node correspondingly.
+//
+// node.Get(key) performs point-query.
+//
+// node.{Min,Max}Key() returns key-range limit for all children/values under the node.
+//
+// node.Entryv() returns [] of (key, child/value).
+//
+// --------
+//
+// (*) https://github.com/zopefoundation/ZODB/blob/3.10.7-4-gb8d7a8567/src/BTrees/Development.txt#L211
+//
+// (+) https://github.com/zopefoundation/ZODB/blob/3.10.7-4-gb8d7a8567/src/BTrees/Development.txt#L231
 package btree
 
 //go:generate ./gen-btree IO int32 ziobtree.go

go/zodb/btree/gen-btree

@@ -2,7 +2,7 @@
 # btree.go.in -> specialized with concrete types
 # gen-btree KIND KEY out
 
-# Copyright (C) 2017  Nexedi SA and Contributors.
+# Copyright (C) 2018  Nexedi SA and Contributors.
 #                     Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute