Thoughts: Add retry and rebalance/rebuild nodes.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

diff --git a/Thoughts b/Thoughts
index aa0f534677afd03e5234a9ba80302a33cfc76ce3..ebba927f3016b49e24cc56f5816a560da3294f01 100644 (file)
--- a/Thoughts
+++ b/Thoughts
@@ -201,6 +201,23 @@ pointer.  Upon allocation failures, the node will continue to contain the
 XA_DELETED_ENTRY and the parent may require an XA_SKIP_ENTRY if a node is
 freed.  Any gaps that can be combined will be done at the start of a node.
 
+When coalescing, a value may be relocated to a different sub-tree.  In this
+case, a reader may already be on its way down and 'miss' the move.  To avoid
+this issue, the special value XA_RETRY_ENTRY is used to indicate a value has
+been moved and the walk operation must restart from the root node.
+
+
+Rebalance & Replacing
+---------------------
+
+Rebalancing occurs if a non-leaf node does not have the minimum number of
+occupied slots.  Rebalancing occurs by consuming data in the node to the right
+into this node.  If there is no data left, the right node is freed.  If there
+is no right node, then rebalancing is done for the left node.  If there is a
+single node, then the trees height is reduced.  When a node is freed, the
+parent is also checked for rebalancing.
+
+Replacing a tree is rarely necessary, however, in the case of a store operation causing an hugely unbalanced tree to be produced, then a rebuild is currently used to restore a compliant B-tree.  ***Note that this will be revisited and replaced.***
 
 Worked examples
 ===============