X ΔBtail: Goodbye .KVAtTail

Use ΔValue.Old for closest to tail entry instead.

wcfs/internal/xbtree/δbtail.go

@@ -117,9 +117,6 @@ type ΔTtail struct {
 	trackNew blib.PPTreeSubSet
 	// XXX + trackNewKeys RangedKeySet
 
-	// {}k/v @tail for keys that are changed in (tail, head].
-	KVAtTail map[Key]Value		// XXX not needed since vδT has ΔValue ?
-
 	// index for LastRevOf queries
 	lastRevOf map[Key]zodb.Tid // {} key -> last
 }
@@ -168,7 +165,6 @@ func NewΔBtail(at0 zodb.Tid, db *zodb.DB) *ΔBtail {
 func newΔTtail() *ΔTtail {
 	return &ΔTtail{
 		trackNew:  blib.PPTreeSubSet{},
-		KVAtTail:  make(map[Key]Value),
 		lastRevOf: make(map[Key]zodb.Tid),
 	}
 }
@@ -211,10 +207,6 @@ func (orig *ΔTtail) Clone() *ΔTtail {
 	klon := &ΔTtail{}
 	klon.vδT = vδTClone(orig.vδT)
 	klon.trackNew = orig.trackNew.Clone()
-	klon.KVAtTail = make(map[Key]Value, len(orig.KVAtTail))
-	for k, v := range orig.KVAtTail {
-		klon.KVAtTail[k] = v
-	}
 	klon.lastRevOf = make(map[Key]zodb.Tid, len(orig.lastRevOf))
 	for k, rev := range orig.lastRevOf {
 		klon.lastRevOf[k] = rev
@@ -389,7 +381,7 @@ func (δTtail *ΔTtail) rebuild(root zodb.Oid, δZtail *zodb.ΔTail, db *zodb.DB
 				δrevSet.Add(δZ.Rev)
 			}
 
-			// XXX update .KVAtTail, .lastRevOf
+			// XXX update .lastRevOf
 		}
 
 		// an iteration closer to tail may turn out to add a key to the tracking set.
@@ -546,7 +538,7 @@ func (δTtail *ΔTtail) rebuild1(atPrev zodb.Tid, δZ zodb.ΔRevEntry, trackNew
 		}
 	}
 
-	// XXX update .KVAtTail, .lastRevOf	(here?)
+	// XXX update .lastRevOf	(here?)
 	return δtrack, δtkeycov, newRevEntry, nil
 }
 
@@ -600,7 +592,6 @@ func (δBtail *ΔBtail) Update(δZ *zodb.EventCommit) (_ ΔB, err error) {
 			}
 		}
 
-		// XXX rebuild KVAtTail
 		// XXX rebuild lastRevOf
 	}
 
@@ -741,7 +732,7 @@ func (δBtail *ΔBtail) ForgetPast(revCut zodb.Tid) {
 }
 
 func (δTtail *ΔTtail) forgetPast(revCut zodb.Tid) {
-	// XXX KVAtTail, lastRevOf
+	// XXX lastRevOf
 
 	icut := 0
 	for ; icut < len(δTtail.vδT); icut++ {
@@ -810,13 +801,6 @@ func (δBtail *ΔBtail) GetAt(ctx context.Context, root *Tree, key Key, at zodb.
 
 	// key not in history tail at all.
 	// use @head[key]
-/*
-	// XXX kill KVAtTail completely
-	value, ok = δTtail.KVAtTail[key] // XXX kill - just use δvalue.Old from next-to-at entry
-	if ok {
-		return
-	}
-*/
 
 	// @tail[key] is not present - key was not changing in (tail, head].
 	// since at ∈ (tail, head] we can use @head[key] as the result

wcfs/internal/xbtree/δbtail_test.go

@@ -1564,7 +1564,7 @@ func _KAdj(t1, t2 *xbtreetest.Commit, keysv ...setKey) (kadj KAdjMatrix) {
 // it also verifies that δbtail.vδBroots matches ΔTtail data.
 func assertΔTtail(t *testing.T, subj string, δbtail *ΔBtail, tj *xbtreetest.Commit, treeRoot zodb.Oid, xat map[zodb.Tid]string, vδTok ...map[Key]Δstring) {
 	t.Helper()
-	// XXX +KVAtTail, +lastRevOf
+	// XXX +lastRevOf
 
 	l := len(vδTok)
 	var vatOK  []zodb.Tid