.

wcfs/δbtail.go

@@ -716,6 +716,11 @@ func diffT(ctx context.Context, A, B *Tree, δZTC SetOid, trackIdx map[zodb.Oid]
 	Akdone  := SetKey{} // already processed keys in A
 	Bkdone  := SetKey{} // ----//---- in B
 
+	// {} oid -> parent for all nodes in Bv: current and previously expanded - up till top B
+	// XXX
+	// XXX requires A.oid == B.oid
+	BtrackIdx := map[zodb.Oid]nodeTrack{B.POid(): nodeTrack{parent: trackIdx[B.POid()].parent}}
+
 	// phase 1: expand A top->down driven by δZTC.
 	// by default a node contributes to δ-
 	// a node ac does not contribute to δ- and can be skipped, if:
@@ -743,7 +748,7 @@ func diffT(ctx context.Context, A, B *Tree, δZTC SetOid, trackIdx map[zodb.Oid]
 
 		case *Tree:
 			// a is tree - expand it and queue children
-			// see for each children whether it can be skipped
+			// check for each children whether it can be skipped
 			// XXX if a is ø tree
 			achildren := Av.Expand(ra)
 			for _, ac := range achildren {
@@ -755,9 +760,36 @@ func diffT(ctx context.Context, A, B *Tree, δZTC SetOid, trackIdx map[zodb.Oid]
 				}
 
 				if !δZTC.Has(acOid) {
-					// XXX also check b's parents, as they could be already expanded?
-					bc, ok, err := Bv.tryGetToNode(acOid, ac.lo, ac.hi_, /*maxdepth*/2)
-					if err != nil { return nil, err }
+					// check B children for node with ac.oid
+					// while checking expand Bv till ac.lo and ac.hi_ point to the same node
+					// ( this does not give exact answer but should be a reasonable heuristic;
+					//   the diff is the same if heuristic does not work and we
+					//   look into and load more nodes to compute δ )
+					_, ok := BtrackIdx[acOid]
+					if !ok {
+						for {
+							blo  := Bv.Get(ac.lo)
+							bhi_ := Bv.Get(ac.hi_)
+							if blo != bhi_ {
+								break
+							}
+							err = blo.node.PActivate(ctx);  /*X*/if err != nil { return nil, err }
+							defer blo.node.PDeactivate()
+
+							bchildren := Bv.Expand(blo)
+							found := false
+							for _, bc := range bchildren {
+									bcOid := bc.node.POid()
+									BtrackIdx[bcOid] = nodeTrack{parent: blo.node.POid()}
+									if acOid == bcOid {
+											found = true
+									}
+							}
+							if found {
+								break
+							}
+						}
+					}
 					if ok {
 						// ac can be skipped
 						// XXX Bkqueue <- holes(ac.range \ bc.range)