some plans

doc/planning.md

@@ -48,3 +48,20 @@ Planning
   - Possible pitfalls when I want to make major changes to
     word-scraper, because I'll have to change two projects. So it is
     probably best to work mainly on b-plus-tree
+
+# May 2, 2014
+
+## Delayed Persistence
+- Instead of writing each node to disc each time one is altered, have
+  a hash-map, mapping RAF offsets to nodes which have already been
+  read and/or altered
+- Whenever a node needs to be read off the disc, first check if its
+  offset is already in the hash-map, and use the in-memory node
+  instead if one exists
+- Instead of simply using `assoc` to add new nodes to the map, write a
+  function which checks the number of elements in the map, and if it
+  reaches a certain threshold (a parameter to the function), write
+  half of the nodes at random to disc, and `dissoc` them from the map
+  after they've been written
+- When all operations are finished, write the entire hash-map to disc,
+  and let it be garbage-collected