From 9249dc18319e83b5757342077f28d6ba08e105df Mon Sep 17 00:00:00 2001
From: Naman Jain <naman@dgraph.io>
Date: Wed, 9 Sep 2020 17:42:44 +0530
Subject: [PATCH] Fix Sequence generates duplicate values (#1281) (#1500)

Fix issue https://github.com/dgraph-io/badger/issues/1280

(cherry picked from commit fa94030a483889c25ce32443ef72c8254b3d294b)

Co-authored-by: GameXG <GameXG@Gmail.com>
---
 db.go      | 23 ++++++++++++++++++++---
 db_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/db.go b/db.go
index 6d9cbb123..bc7023eb1 100644
--- a/db.go
+++ b/db.go
@@ -1110,9 +1110,26 @@ func (seq *Sequence) Release() error {
 	seq.Lock()
 	defer seq.Unlock()
 	err := seq.db.Update(func(txn *Txn) error {
-		var buf [8]byte
-		binary.BigEndian.PutUint64(buf[:], seq.next)
-		return txn.SetEntry(NewEntry(seq.key, buf[:]))
+		item, err := txn.Get(seq.key)
+		if err != nil {
+			return err
+		}
+
+		var num uint64
+		if err := item.Value(func(v []byte) error {
+			num = binary.BigEndian.Uint64(v)
+			return nil
+		}); err != nil {
+			return err
+		}
+
+		if num == seq.leased {
+			var buf [8]byte
+			binary.BigEndian.PutUint64(buf[:], seq.next)
+			return txn.SetEntry(NewEntry(seq.key, buf[:]))
+		}
+
+		return nil
 	})
 	if err != nil {
 		return err
diff --git a/db_test.go b/db_test.go
index 2ecc660be..f47d598ad 100644
--- a/db_test.go
+++ b/db_test.go
@@ -1373,6 +1373,33 @@ func TestSequence_Release(t *testing.T) {
 	})
 }
 
+func TestTestSequence2(t *testing.T) {
+	runBadgerTest(t, nil, func(t *testing.T, db *DB) {
+		key := []byte("key")
+		seq1, err := db.GetSequence(key, 2)
+		require.NoError(t, err)
+
+		seq2, err := db.GetSequence(key, 2)
+		require.NoError(t, err)
+		num, err := seq2.Next()
+		require.NoError(t, err)
+		require.Equal(t, uint64(2), num)
+
+		require.NoError(t, seq2.Release())
+		require.NoError(t, seq1.Release())
+
+		seq3, err := db.GetSequence(key, 2)
+		require.NoError(t, err)
+		for i := 0; i < 5; i++ {
+			num2, err := seq3.Next()
+			require.NoError(t, err)
+			require.Equal(t, uint64(i)+3, num2)
+		}
+
+		require.NoError(t, seq3.Release())
+	})
+}
+
 func TestReadOnly(t *testing.T) {
 	dir, err := ioutil.TempDir("", "badger-test")
 	require.NoError(t, err)