.

wcfs/internal/xbtree/δbtail.go

@@ -101,6 +101,7 @@ type Key    = int64
 type ΔTail struct {
 	δBtail []ΔRevEntry // BTree changes; Covers keys ∈ tracket subset
 	δZtail *zodb.ΔTail // raw ZODB changes; Kept to rebuild δBtail after new Track
+//	head   zodb.Tid    // δBtail currently has coverage till head], δZtail can have more
 
 	// XXX or ask client provide db on every call?
 	db     *zodb.DB    // to open connections to load new/old tree|buckets
@@ -135,7 +136,7 @@ func NewΔTail(at0 zodb.Tid) *ΔTail {
 
 // Head is similar to zodb.ΔTail.Head .		XXX ok?
 func (δb *ΔTail) Head() zodb.Tid {
-	return δb.δZtail.Head()
+	return δb.head
 }
 
 // Tail is similar to zodb.ΔTail.Tail .		XXX ok?
@@ -174,6 +175,13 @@ func (δb *ΔTail) Track(path []Node) {	// XXX Tree|Bucket; path[0] = root
 func (δB *ΔTail) Update(δZ *zodb.EventCommit) {
 /*
 	.δZtail += δZ
+	.update()
+*/
+
+// update brings .δBtail up to date by recomputing diff XXX and taking new
+// entries in .δZtail into account.
+func (δB *ΔTail) update() {
+/*
 	δbZ = {}
 	for δ in δZ:
 		.rootIdx[δ]: