fix(pendingWrites): don't skip the pending entries with version=0 (#1721

)

With the introduction of SinceTs, a bug was introduced #1653 that skips the pending entries.
The default value of SinceTs is zero. And for the transaction made at readTs 0, the pending entries have version set to 0. So they were also getting skipped.

(cherry picked from commit 3911787)

iterator.go

@@ -638,7 +638,7 @@ func (it *Iterator) parseItem() bool {
 	// Skip any versions which are beyond the readTs.
 	version := y.ParseTs(key)
 	// Ignore everything that is above the readTs and below or at the sinceTs.
-	if version > it.readTs || version <= it.opt.SinceTs {
+	if version > it.readTs || (it.opt.SinceTs > 0 && version <= it.opt.SinceTs) {
 		mi.Next()
 		return false
 	}

iterator_test.go

@@ -160,6 +160,24 @@ func TestIterateSinceTs(t *testing.T) {
 	})
 }
 
+func TestIterateSinceTsWithPendingWrites(t *testing.T) {
+	// The pending entries still have version=0. Even IteratorOptions.SinceTs is 0, the entries
+	// should be visible.
+	runBadgerTest(t, nil, func(t *testing.T, db *DB) {
+		txn := db.NewTransaction(true)
+		defer txn.Discard()
+		require.NoError(t, txn.Set([]byte("key1"), []byte("value1")))
+		require.NoError(t, txn.Set([]byte("key2"), []byte("value2")))
+		itr := txn.NewIterator(DefaultIteratorOptions)
+		defer itr.Close()
+		count := 0
+		for itr.Rewind(); itr.Valid(); itr.Next() {
+			count++
+		}
+		require.Equal(t, 2, count)
+	})
+}
+
 func TestIteratePrefix(t *testing.T) {
 	if !*manual {
 		t.Skip("Skipping test meant to be run manually.")