Initial head_only features

Initial commit to add head_only mode to leveled.  This allows leveled to receive batches of object changes, but where those objects exist only in the Penciller's Ledger (once they have been persisted within the Ledger).

The aim is to reduce significantly the cost of compaction.  Also, the objects ar enot directly accessible (they can only be accessed through folds).  Again this makes life easier during merging in the LSM trees (as no bloom filters have to be created).

src/leveled_codec.erl

@@ -62,6 +62,7 @@
         get_size/2,
         get_keyandobjhash/2,
         idx_indexspecs/5,
+        obj_objectspecs/3,
         aae_indexspecs/6,
         generate_uuid/0,
         integer_now/0,
@@ -222,7 +223,7 @@ from_ledgerkey({?IDX_TAG, ?ALL_BUCKETS, {_IdxFld, IdxVal}, {Bucket, Key}}) ->
     {Bucket, Key, IdxVal};
 from_ledgerkey({?IDX_TAG, Bucket, {_IdxFld, IdxVal}, Key}) ->
     {Bucket, Key, IdxVal};
-from_ledgerkey({_Tag, Bucket, Key, null}) ->
+from_ledgerkey({_Tag, Bucket, Key, _SubKey}) ->
     {Bucket, Key}.
 
 to_ledgerkey(Bucket, Key, Tag, Field, Value) when Tag == ?IDX_TAG ->
@@ -231,6 +232,9 @@ to_ledgerkey(Bucket, Key, Tag, Field, Value) when Tag == ?IDX_TAG ->
 to_ledgerkey(Bucket, Key, Tag) ->
     {Tag, Bucket, Key, null}.
 
+to_ledgerkey(Bucket, Key, Tag, SubKey) ->
+        {Tag, Bucket, Key, SubKey}.
+
 %% Return the Key, Value and Hash Option for this object.  The hash option
 %% indicates whether the key would ever be looked up directly, and so if it
 %% requires an entry in the hash table
@@ -404,6 +408,8 @@ split_inkvalue(VBin) when is_binary(VBin) ->
 
 check_forinkertype(_LedgerKey, delete) ->
     ?INKT_TOMB;
+check_forinkertype(_LedgerKey, head_only) ->
+    ?INKT_MPUT;
 check_forinkertype(_LedgerKey, _Object) ->
     ?INKT_STND.
 
@@ -424,6 +430,14 @@ endkey_passed({EK1, EK2, EK3, null}, {CK1, CK2, CK3, _}) ->
 endkey_passed(EndKey, CheckingKey) ->
     EndKey < CheckingKey.
 
+
+obj_objectspecs(ObjectSpecs, SQN, TTL) ->
+    lists:map(fun({IdxOp, Bucket, Key, SubKey, Value}) ->
+                    gen_headspec(Bucket, Key, IdxOp, SubKey, Value, SQN, TTL)
+                end,
+                ObjectSpecs).
+
+
 idx_indexspecs(IndexSpecs, Bucket, Key, SQN, TTL) ->
     lists:map(
             fun({IdxOp, IdxFld, IdxTrm}) ->
@@ -458,6 +472,19 @@ gen_indexspec(Bucket, Key, IdxOp, IdxField, IdxTerm, SQN, TTL) ->
                 {SQN, Status, no_lookup, null}}
     end.
 
+gen_headspec(Bucket, Key, IdxOp, SubKey, Value, SQN, TTL) ->
+    Status =
+        case IdxOp of
+            add ->
+                {active, TTL};
+            remove ->
+                %% TODO: timestamps for delayed reaping 
+                tomb
+        end,
+    {to_ledgerkey(Bucket, Key, ?HEAD_TAG, SubKey),
+        {SQN, Status, no_lookup, Value}}.
+
+
 -spec aae_indexspecs(false|recent_aae(),
                                 any(), any(),
                                 integer(), integer(),
@@ -611,7 +638,9 @@ get_size(PK, Value) ->
             Size;
         ?STD_TAG ->
             {_Hash, Size} = MD,
-            Size
+            Size;
+        ?HEAD_TAG ->
+            0
     end.
 
 -spec get_keyandobjhash(tuple(), tuple()) -> tuple().
@@ -641,12 +670,14 @@ get_objhash(Tag, ObjMetaData) ->
         
 
 build_metadata_object(PrimaryKey, MD) ->
-    {Tag, _Bucket, _Key, null} = PrimaryKey,
+    {Tag, _Bucket, _Key, _SubKey} = PrimaryKey,
     case Tag of
         ?RIAK_TAG ->
             {SibData, Vclock, _Hash, _Size} = MD,
             riak_metadata_to_binary(Vclock, SibData);
         ?STD_TAG ->
+            MD;
+        ?HEAD_TAG ->
             MD
     end.