router: fix connection score becomes wrong when a connection closes d…

…uring redirecting (#451)

pkg/manager/router/router.go

@@ -139,7 +139,9 @@ func (b *backendWrapper) String() string {
 // connWrapper wraps RedirectableConn.
 type connWrapper struct {
 	RedirectableConn
-	phase connPhase
+	// Reference to the target backend if it's redirecting, otherwise nil.
+	redirectingBackend *backendWrapper
 	// Last redirect start time of this connection.
 	lastRedirect time.Time
+	phase        connPhase
 }

pkg/manager/router/router_score.go

@@ -190,6 +190,7 @@ func (router *ScoreBasedRouter) RedirectConnections() error {
 				connWrapper.phase = phaseRedirectNotify
 				// we dont care the results
 				_ = connWrapper.Redirect(backend)
+				connWrapper.redirectingBackend = backend
 			}
 		}
 	}
@@ -263,18 +264,25 @@ func (router *ScoreBasedRouter) onRedirectFinished(from, to string, conn Redirec
 		router.adjustBackendList(toBe, true)
 		connWrapper.phase = phaseRedirectFail
 	}
+	connWrapper.redirectingBackend = nil
 	addMigrateMetrics(from, to, succeed, connWrapper.lastRedirect)
 }
 
 // OnConnClosed implements ConnEventReceiver.OnConnClosed interface.
 func (router *ScoreBasedRouter) OnConnClosed(addr string, conn RedirectableConn) error {
 	router.Lock()
 	defer router.Unlock()
-	// OnConnClosed is always called after processing ongoing redirect events,
-	// so the addr passed in is the right backend.
 	be := router.ensureBackend(addr, true)
-	be.Value.connScore--
-	router.removeConn(be, router.getConnWrapper(conn))
+	connWrapper := router.getConnWrapper(conn)
+	redirectingBackend := connWrapper.Value.redirectingBackend
+	// If this connection is redirecting, decrease the score of the target backend.
+	if redirectingBackend != nil {
+		redirectingBackend.connScore--
+		connWrapper.Value.redirectingBackend = nil
+	} else {
+		be.Value.connScore--
+	}
+	router.removeConn(be, connWrapper)
 	return nil
 }
 
@@ -375,6 +383,7 @@ func (router *ScoreBasedRouter) rebalance(maxNum int) {
 		conn.phase = phaseRedirectNotify
 		conn.lastRedirect = curTime
 		conn.Redirect(idlestBackend)
+		conn.redirectingBackend = idlestBackend
 	}
 }
 

pkg/manager/router/router_test.go

@@ -900,3 +900,23 @@ func TestBackendHealthy(t *testing.T) {
 	require.False(t, conn.to.Healthy())
 	tester.redirectFinish(1, false)
 }
+
+func TestCloseRedirectingConns(t *testing.T) {
+	// Make the connection redirect.
+	tester := newRouterTester(t)
+	tester.addBackends(1)
+	tester.addConnections(1)
+	require.Equal(t, 1, tester.getBackendByIndex(0).connScore)
+	tester.killBackends(1)
+	tester.addBackends(1)
+	tester.rebalance(1)
+	require.Equal(t, 0, tester.getBackendByIndex(0).connScore)
+	require.Equal(t, 1, tester.getBackendByIndex(1).connScore)
+	// Close the connection.
+	tester.updateBackendStatusByAddr(tester.getBackendByIndex(0).Addr(), StatusHealthy)
+	tester.closeConnections(1, true)
+	require.Equal(t, 0, tester.getBackendByIndex(0).connScore)
+	require.Equal(t, 0, tester.getBackendByIndex(1).connScore)
+	require.Equal(t, 0, tester.getBackendByIndex(0).connList.Len())
+	require.Equal(t, 0, tester.getBackendByIndex(1).connList.Len())
+}