X notes on why lazy-invalidate approach was taken

wcfs/wcfs.go

@@ -343,6 +343,13 @@ package main
 // XXX zconn(s) for historical state
 // XXX serving read from @<rev>/data
 //
+// XXX(integrate place=?) emitting whole δR right at transaction-boundary time
+// requires to keep whole blktab index in tree. Even though from space point of
+// view it is somewhat acceptable (~ 0.01% of whole-file data size, i.e. ~
+// 128MB of index for ~ 1TB of data), it is not good from time overhead point
+// of view - initial open of a file this way would be potentially very slow.
+// -> we took the approach where we invalidate lazily only actual block access.
+//
 // XXX(integrate place=?) ZData - ne need to keep track -> ZBlk1 is always
 // marked as changed on blk data change.
 //