main.go

@@ -26,7 +26,6 @@ type Store struct {
 type Transaction struct {
 	store       *Store
 	readTS      Timestamp
-	readSet     map[string]struct{}
 	writeBuffer map[string]string
 	committed   bool
 }
@@ -66,13 +65,11 @@ func (s *Store) Begin() *Transaction {
 	return &Transaction{
 		store:       s,
 		readTS:      readTS,
-		readSet:     make(map[string]struct{}),
 		writeBuffer: make(map[string]string),
 	}
 }
 
 func (tx *Transaction) Read(key string) (string, bool) {
-	tx.readSet[key] = struct{}{}
 	if val, ok := tx.writeBuffer[key]; ok {
 		return val, true
 	}
@@ -88,40 +85,27 @@ func (tx *Transaction) Commit() error {
 		return fmt.Errorf("transaction already committed")
 	}
 
-	s := tx.store
+	tx.store.mu.Lock()
-	s.mu.Lock()
+	defer tx.store.mu.Unlock()
-	defer s.mu.Unlock()
 
-	getLatestTS := func(key string) Timestamp {
+	// Conflict detection
-		if h, ok := s.data[key]; ok && len(h.Versions) > 0 {
-			return h.Versions[len(h.Versions)-1].Timestamp
-		}
-		return 0
-	}
-
-	// Write-write Conflict detection
 	for key := range tx.writeBuffer {
-		if getLatestTS(key) > tx.readTS {
+		history, exists := tx.store.data[key]
-			return fmt.Errorf("write-write conflict on key: %s", key)
+		if !exists {
-		}
-	}
-
-	// Read-write conflict detection (excluding keys we're writing)
-	for key := range tx.readSet {
-		if _, isWriting := tx.writeBuffer[key]; isWriting {
 			continue
 		}
-		if getLatestTS(key) > tx.readTS {
+		latest := history.Versions[len(history.Versions)-1]
-			return fmt.Errorf("read-write conflict on key: %s", key)
+		if latest.Timestamp > tx.readTS {
+			return fmt.Errorf("write-write conflict on key '%s'", key)
 		}
 	}
 
 	commitTS := tx.store.nextTimestamp()
 	for key, val := range tx.writeBuffer {
-		history, exists := s.data[key]
+		history, exists := tx.store.data[key]
 		if !exists {
 			history = &KeyHistory{}
-			s.data[key] = history
+			tx.store.data[key] = history
 		}
 		history.Versions = append(history.Versions, VersionedValue{
 			Value:     val,
@@ -155,9 +139,10 @@ func main() {
 		fmt.Println("tx2 reads foo: not found")
 	}
 
-	// Transaction 3: Conflicting write — modifies "foo" after tx2 read it
+	// Transaction 3: Conflicting write
 	tx3 := store.Begin()
 	tx3.Write("foo", "baz")
+	// tx2 committed first, so tx3 will conflict if tx2 also wrote to "foo"
 	err = tx3.Commit()
 	if err != nil {
 		fmt.Println("tx3 commit error:", err)
@@ -165,21 +150,11 @@ func main() {
 		fmt.Println("tx3 committed")
 	}
 
-	// Now tx2 tries to commit after reading a value that's been modified — should conflict
-	tx2.Write("bar", "new") // tx2 tries to do something unrelated, but it read "foo"
-	err = tx2.Commit()
-	if err != nil {
-		fmt.Println("tx2 commit error (expected read-write conflict):", err)
-	} else {
-		fmt.Println("tx2 committed (unexpected!)")
-	}
-
 	// Transaction 4: Should read latest "foo"
 	tx4 := store.Begin()
 	val, _ = tx4.Read("foo")
 	fmt.Printf("tx4 reads foo: %s\n", val)
 
-	// Additional write-write conflict test (unchanged)
 	tx5 := store.Begin()
 	tx6 := store.Begin()
 
@@ -197,4 +172,3 @@ func main() {
 		fmt.Println("tx6 committed (unexpectedly)")
 	}
 }
-