From 4206c8232f19402c38da6a966a886b9544d85953 Mon Sep 17 00:00:00 2001
From: Harshil Goel <harshil@hypermode.com>
Date: Tue, 15 Apr 2025 09:00:49 +0530
Subject: [PATCH] fix(core): fix old deletes for scalar postings

---
 posting/list.go     | 35 +++++++++----------------
 worker/sort_test.go | 62 ++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 24 deletions(-)

diff --git a/posting/list.go b/posting/list.go
index 07bbd91c03f..2d7fea12a9a 100644
--- a/posting/list.go
+++ b/posting/list.go
@@ -737,6 +737,14 @@ func NewPosting(t *pb.DirectedEdge) *pb.Posting {
 	return p
 }
 
+func createDeleteAllPosting() *pb.Posting {
+	return &pb.Posting{
+		Op:    Del,
+		Value: []byte(x.Star),
+		Uid:   math.MaxUint64,
+	}
+}
+
 func hasDeleteAll(mpost *pb.Posting) bool {
 	return mpost.Op == Del && bytes.Equal(mpost.Value, []byte(x.Star)) && len(mpost.LangTag) == 0
 }
@@ -768,30 +776,11 @@ func (l *List) updateMutationLayer(mpost *pb.Posting, singleUidUpdate, hasCountI
 		// be done because the fingerprint for the value is not math.MaxUint64 as is
 		// the case with the rest of the scalar predicates.
 		newPlist := &pb.PostingList{}
-		newPlist.Postings = append(newPlist.Postings, mpost)
-
-		// Add the deletions in the existing plist because those postings are not picked
-		// up by iterating. Not doing so would result in delete operations that are not
-		// applied when the transaction is committed.
-		l.mutationMap.currentEntries = &pb.PostingList{}
-		err := l.iterate(mpost.StartTs, 0, func(obj *pb.Posting) error {
-			// Ignore values which have the same uid as they will get replaced
-			// by the current value.
-			if obj.Uid == mpost.Uid {
-				return nil
-			}
-
-			// Mark all other values as deleted. By the end of the iteration, the
-			// list of postings will contain deleted operations and only one set
-			// for the mutation stored in mpost.
-			objCopy := proto.Clone(obj).(*pb.Posting)
-			objCopy.Op = Del
-			newPlist.Postings = append(newPlist.Postings, objCopy)
-			return nil
-		})
-		if err != nil {
-			return err
+		if mpost.Op != Del {
+			// If we are setting a new value then we can just delete all the older values.
+			newPlist.Postings = append(newPlist.Postings, createDeleteAllPosting())
 		}
+		newPlist.Postings = append(newPlist.Postings, mpost)
 		l.mutationMap.setCurrentEntries(mpost.StartTs, newPlist)
 		return nil
 	}
diff --git a/worker/sort_test.go b/worker/sort_test.go
index 57d8f1f2173..95b6dee3408 100644
--- a/worker/sort_test.go
+++ b/worker/sort_test.go
@@ -394,7 +394,67 @@ func TestScalarPredicateCount(t *testing.T) {
 	l.RUnlock()
 }
 
-func TestSingleUid(t *testing.T) {
+func TestSingleUidReplacement(t *testing.T) {
+	dir, err := os.MkdirTemp("", "storetest_")
+	x.Check(err)
+	defer os.RemoveAll(dir)
+
+	opt := badger.DefaultOptions(dir)
+	ps, err := badger.OpenManaged(opt)
+	x.Check(err)
+	pstore = ps
+	posting.Init(ps, 0, false)
+	Init(ps)
+	err = schema.ParseBytes([]byte("singleUidReplaceTest: uid ."), 1)
+	require.NoError(t, err)
+
+	ctx := context.Background()
+	txn := posting.Oracle().RegisterStartTs(5)
+	attr := x.GalaxyAttr("singleUidReplaceTest")
+
+	// Txn 1. Set 1 -> 2
+	x.Check(runMutation(ctx, &pb.DirectedEdge{
+		ValueId: 2,
+		Attr:    attr,
+		Entity:  1,
+		Op:      pb.DirectedEdge_SET,
+	}, txn))
+
+	txn.Update()
+	writer := posting.NewTxnWriter(pstore)
+	require.NoError(t, txn.CommitToDisk(writer, 7))
+	require.NoError(t, writer.Flush())
+	txn.UpdateCachedKeys(7)
+
+	// Txn 2. Set 1 -> 3
+	txn = posting.Oracle().RegisterStartTs(9)
+
+	x.Check(runMutation(ctx, &pb.DirectedEdge{
+		ValueId: 3,
+		Attr:    attr,
+		Entity:  1,
+		Op:      pb.DirectedEdge_SET,
+	}, txn))
+
+	txn.Update()
+	writer = posting.NewTxnWriter(pstore)
+	require.NoError(t, txn.CommitToDisk(writer, 11))
+	require.NoError(t, writer.Flush())
+	txn.UpdateCachedKeys(11)
+
+	key := x.DataKey(attr, 1)
+
+	// Reading the david index, we should see 2 inserted, 1 deleted
+	txn = posting.Oracle().RegisterStartTs(15)
+	l, err := txn.Get(key)
+	require.NoError(t, err)
+
+	uids, err := l.Uids(posting.ListOptions{ReadTs: 15})
+	require.NoError(t, err)
+	require.Equal(t, uids.Uids, []uint64{3})
+}
+
+func TestSingleString(t *testing.T) {
 	dir, err := os.MkdirTemp("", "storetest_")
 	x.Check(err)
 	defer os.RemoveAll(dir)