.

wcfs/internal/xbtree/δbtail.go

@@ -22,53 +22,6 @@
 // TODO move -> btree when ΔTail matures.
 package xbtree
 
-// δ(BTree) notes
-// ==============
-//
-// input: BTree, (@new, []oid)  ->  find out δ(BTree) i.e. {-k(v), +k'(v'), ...}
-//
-// - oid ∈ Bucket
-// - oid ∈ BTree
-//
-// Bucket:
-//
-//      old = {k  -> v}
-//      new = {k' -> v'}
-//
-//      Δ = -k(v), +k(v), ...
-//
-// => for all buckets
-//
-//      Δ accumulates to []δk(v)[n+,n-]  n+ ∈ {0,1}, n- ∈ {0,1}, if n+=n- - cancel
-//
-//
-// BTree:
-//
-//      old = {k  -> B}   or {k  -> T}
-//      new = {k' -> B'}  or {k' -> T'}
-//
-//      Δ = -k(B), +k(B), -k(T), +K(T), ...
-//
-// we translate (in top-down order):
-//
-//      k(B) -> {} of k(v)
-//      k(T) -> {} of k(B) -> {} of k(v)
-//
-// which gives
-//
-//      Δ = k(v), +k(v), ...
-//
-// i.e. exactly as for buckets and it accumulates to global Δ.
-//
-// The globally-accumulated Δ is the answer for δ(BTree, (@new, []oid))
-//
-// top-down order is obtained via toposort({oid}) wrt visited PathSet.
-//
-// δ(BTree) in wcfs context:
-//
-// . -k(blk) -> invalidate #blk
-// . +k(blk) -> invalidate #blk (e.g. if blk was previously read as hole)
-
 //go:generate ../../gen-set xbtree Tree *Tree zset_tree.go
 // //go:generate ../../gen-set xbtree Oid zodb.Oid zset_oid.go
 //go:generate ../../gen-set xbtree Object interface{} zset_object.go
@@ -92,6 +45,7 @@ type Value  = zodb.Oid // XXX assumes key points to IPersistent
 //	# trees changed by a revision
 //	[](rev↑, []root)		; rev ∈ (tail, head]
 //
+//	# for every tree:
 //	{} root ->
 //		# k/v change history	; rev ∈ (tail, head]
 //		[](rev↑, {}(key, value))
@@ -101,6 +55,8 @@ type Value  = zodb.Oid // XXX assumes key points to IPersistent
 //
 // A tree nodes become tracked via Track(path) request.
 //
+// XXX which operations are provided.
+//
 // An example for tracked set is a set of visited BTree paths.
 // There is no requirement that tracked set belongs to only one single BTree.
 //
@@ -112,10 +68,10 @@ type Value  = zodb.Oid // XXX assumes key points to IPersistent
 //
 // ΔTail is not safe for concurrent access.
 type ΔTail struct {
-	δZtail *zodb.ΔTail // raw ZODB changes; Kept to rebuild δBtail (XXX) after new Track
+	δZtail *zodb.ΔTail // raw ZODB changes; Kept to rebuild δBtail/byRoot after new Track
 
 	δBtail []ΔRevEntry // which BTree were changed; Noted only by keys ∈ tracket subset
-	byRoot map[*Tree]*ΔTreeTail
+	byRoot map[*Tree]*ΔTreeTail // root -> k/v change history; only for keys ∈ tracket subset
 
 	// XXX or ask client provide db on every call?
 	db     *zodb.DB    // to open connections to load new/old tree|buckets
@@ -291,3 +247,51 @@ func (btail *ΔTail) LastRevOf(root *Tree, key Key, at zodb.Tid) (_ zodb.Tid, ex
 func (btail *ΔTail) ForgetPast(revCut zodb.Tid) {
 	btail.δZtail.ForgetPast(revCut) // XXX stub
 }
+
+
+// δ(BTree) notes
+// ==============
+//
+// input: BTree, (@new, []oid)  ->  find out δ(BTree) i.e. {-k(v), +k'(v'), ...}
+//
+// - oid ∈ Bucket
+// - oid ∈ BTree
+//
+// Bucket:
+//
+//      old = {k  -> v}
+//      new = {k' -> v'}
+//
+//      Δ = -k(v), +k(v), ...
+//
+// => for all buckets
+//
+//      Δ accumulates to []δk(v)[n+,n-]  n+ ∈ {0,1}, n- ∈ {0,1}, if n+=n- - cancel
+//
+//
+// BTree:
+//
+//      old = {k  -> B}   or {k  -> T}
+//      new = {k' -> B'}  or {k' -> T'}
+//
+//      Δ = -k(B), +k(B), -k(T), +K(T), ...
+//
+// we translate (in top-down order):
+//
+//      k(B) -> {} of k(v)
+//      k(T) -> {} of k(B) -> {} of k(v)
+//
+// which gives
+//
+//      Δ = k(v), +k(v), ...
+//
+// i.e. exactly as for buckets and it accumulates to global Δ.
+//
+// The globally-accumulated Δ is the answer for δ(BTree, (@new, []oid))
+//
+// top-down order is obtained via toposort({oid}) wrt visited PathSet.
+//
+// δ(BTree) in wcfs context:
+//
+// . -k(blk) -> invalidate #blk
+// . +k(blk) -> invalidate #blk (e.g. if blk was previously read as hole)