X δbtail: tests: Tweaks to run rebuild tests faster

        $ time go test -failfast -short -run 'ΔBTail/rebuild' >x

before:

        real    0m17,852s
        user    0m23,068s
        sys     0m1,825s

after:

        real    0m9,622s
        user    0m12,515s
        sys     0m1,274s

wcfs/set.go.in

@@ -59,7 +59,14 @@ func (s Set) Elements() []VALUE {
 
 // Union returns s ∪ t
 func (s Set) Union(t Set) Set {
-	u := Set{}
+	// l = max(len(s), len(t))
+	l := len(s)
+	if lt := len(t); lt > l {
+		l = lt
+	}
+
+	u := make(Set, l)
+
 	for v := range s {
 		u.Add(v)
 	}

wcfs/zset_bigfile.go

@@ -61,7 +61,14 @@ func (s SetBigFile) Elements() []*BigFile {
 
 // Union returns s ∪ t
 func (s SetBigFile) Union(t SetBigFile) SetBigFile {
-	u := SetBigFile{}
+	// l = max(len(s), len(t))
+	l := len(s)
+	if lt := len(t); lt > l {
+		l = lt
+	}
+
+	u := make(SetBigFile, l)
+
 	for v := range s {
 		u.Add(v)
 	}

wcfs/zset_i64.go

@@ -61,7 +61,14 @@ func (s SetI64) Elements() []int64 {
 
 // Union returns s ∪ t
 func (s SetI64) Union(t SetI64) SetI64 {
-	u := SetI64{}
+	// l = max(len(s), len(t))
+	l := len(s)
+	if lt := len(t); lt > l {
+		l = lt
+	}
+
+	u := make(SetI64, l)
+
 	for v := range s {
 		u.Add(v)
 	}

wcfs/zset_oid.go

@@ -61,7 +61,14 @@ func (s SetOid) Elements() []Oid {
 
 // Union returns s ∪ t
 func (s SetOid) Union(t SetOid) SetOid {
-	u := SetOid{}
+	// l = max(len(s), len(t))
+	l := len(s)
+	if lt := len(t); lt > l {
+		l = lt
+	}
+
+	u := make(SetOid, l)
+
 	for v := range s {
 		u.Add(v)
 	}

wcfs/δbtail.go

@@ -451,28 +451,35 @@ func NewΔBtail(at0 zodb.Tid, db *zodb.DB) *ΔBtail {
 
 // xverifyΔBTail_rebuild needs ΔBTree.clone because otherwise it is too slow to run that test.
 func (orig *ΔBtail) clone() *ΔBtail {
-	klon := NewΔBtail(orig.Tail(), orig.db)
+	klon := &ΔBtail{db: orig.db}
+
 	// δZtail
+	klon.δZtail = zodb.NewΔTail(orig.Tail())
 	for _, δZ := range orig.δZtail.Data() {
 		klon.δZtail.Append(δZ.Rev, δZ.Changev)
 	}
 
 	// trackIdx
+	klon.trackIdx = make(trackIndex, len(orig.trackIdx))
 	for oid, t := range orig.trackIdx {
 		klon.trackIdx[oid] = &nodeTrack{parent: t.parent, nchild: t.nchild}
 	}
 	// trackNew
+	klon.trackNew = make(trackIndex, len(orig.trackNew))
 	for oid, t := range orig.trackNew {
 		klon.trackNew[oid] = &nodeTrack{parent: t.parent, nchild: t.nchild}
 	}
 
 	// byRoot
+	klon.byRoot = make(map[zodb.Oid]*ΔTtail, len(orig.byRoot))
 	for root, origΔTtail := range orig.byRoot {
 		klonΔTtail := &ΔTtail{}
 		klonΔTtail.vδT = append(klonΔTtail.vδT, origΔTtail.vδT...)
+		klonΔTtail.KVAtTail = make(map[Key]Value, len(origΔTtail.KVAtTail))
 		for k, v := range origΔTtail.KVAtTail {
 			klonΔTtail.KVAtTail[k] = v
 		}
+		klonΔTtail.lastRevOf = make(map[Key]zodb.Tid, len(origΔTtail.lastRevOf))
 		for k, rev := range origΔTtail.lastRevOf {
 			klonΔTtail.lastRevOf[k] = rev
 		}
@@ -480,8 +487,9 @@ func (orig *ΔBtail) clone() *ΔBtail {
 	}
 
 	// holeIdxByRoot
+	klon.holeIdxByRoot = make(map[zodb.Oid]treeSetKey, len(orig.holeIdxByRoot))
 	for root, origHoleIdx := range orig.holeIdxByRoot {
-		klonHoleIdx := treeSetKey{SetKey{}}
+		klonHoleIdx := treeSetKey{make(SetKey, len(origHoleIdx.SetKey))}
 		klonHoleIdx.Update(origHoleIdx.SetKey)
 		klon.holeIdxByRoot[root] = klonHoleIdx
 	}
@@ -1617,7 +1625,7 @@ func vnode(node Node) string {
 	case *Tree:   kind = "T"
 	case *Bucket: kind = "B"
 	}
-	return fmt.Sprintf("%s%s", kind, node.POid())
+	return kind + node.POid().String()
 }
 
 func (rn nodeInRange) String() string {

wcfs/δbtail_test.go

@@ -822,11 +822,34 @@ func xverifyΔBTail_Update1(t *testing.T, subj string, db *zodb.DB, treeRoot zod
 	}
 }
 
+// equal returns whether a == b.
+// XXX place
+func (a trackIndex) equal(b trackIndex) bool {
+	if len(a) != len(b) {
+		return false
+	}
+
+	for oid, ta := range a {
+		tb, ok := b[oid]
+		if !ok {
+			return false
+		}
+
+		if !(ta.parent == tb.parent && ta.nchild == tb.nchild) {
+			return false
+		}
+	}
+
+	return true
+}
+
 // assertTrack verifies that trackIdx == trackIdxOK.
 // XXX place
 func assertTrack(t *testing.T, subj string, trackIdx, trackIdxOK trackIndex) {
 	t.Helper()
-	if !reflect.DeepEqual(trackIdx, trackIdxOK) {
+	// eq := reflect.DeepEqual(trackIdx, trackIdxOK) // slower
+	eq := trackIdx.equal(trackIdxOK)
+	if !eq {
 		t.Errorf("%s:\n\thave: %v\n\twant: %v", subj, trackIdx, trackIdxOK)
 	}
 }
@@ -899,7 +922,7 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 					/*trackIdx=*/ t1.xkv.trackIdx(keys1),
 					/*vδB=*/      /*XXX temp*/nil /*[δ1/Tadj(keys1)*/)
 
-				t.Run(fmt.Sprintf(" →%s", t2.tree), func(t *testing.T) {
+				t.Run((" →" + t2.tree), func(t *testing.T) {
 					// tracked keys1 becomes tracked keys1_2 after Update(t1->t2)
 					keys1_2 := kadj12.Map(keys1)
 					xverifyΔBTail_rebuild_U(t, δbtail, t1, t2, xat, /*trackIdx=*/t2.xkv.trackIdx(keys1_2))
@@ -913,7 +936,8 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 							keys2.Add(tRestKeyv2[idx2])
 						}
 
-						t.Run(fmt.Sprintf(" T%s;R", keys2), func(t *testing.T) {
+						// t.Run is expensive at this level of nest
+//						t.Run(" T"+keys2.String()+";R", func(t *testing.T) {
 							δbtail_ := δbtail.clone()
 							xverifyΔBTail_rebuild_TR(t, db, δbtail_, t2, treeRoot, xat,
 								// after Track(keys2)
@@ -925,7 +949,7 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 								// after rebuild
 								/* trackIdx=*/ t2.xkv.trackIdx(keys1_2.Union(keys2)),
 								/*vδB=*/      /*XXX temp*/nil /*[δ1/keys1+keys2, δ2/keys1+keys2]*/)
-						})
+//						})
 					}
 				})
 			})