[release-19.0] VReplication: Address SwitchTraffic bugs around replication lag and cancel on error (#17616)

go/test/endtoend/vreplication/cluster_test.go

@@ -886,7 +886,7 @@ func (vc *VitessCluster) getVttabletsInKeyspace(t *testing.T, cell *Cell, ksName
 	tablets := make(map[string]*cluster.VttabletProcess)
 	for _, shard := range keyspace.Shards {
 		for _, tablet := range shard.Tablets {
-			if tablet.Vttablet.GetTabletStatus() == "SERVING" {
+			if tablet.Vttablet.GetTabletStatus() == "SERVING" && (tabletType == "" || strings.EqualFold(tablet.Vttablet.GetTabletType(), tabletType)) {
 				log.Infof("Serving status of tablet %s is %s, %s", tablet.Name, tablet.Vttablet.ServingStatus, tablet.Vttablet.GetTabletStatus())
 				tablets[tablet.Name] = tablet.Vttablet
 			}

go/test/endtoend/vreplication/vreplication_test.go

@@ -762,11 +762,16 @@ func shardCustomer(t *testing.T, testReverse bool, cells []*Cell, sourceCellOrAl
 		switchReads(t, workflowType, cellNames, ksWorkflow, false)
 		assertQueryExecutesOnTablet(t, vtgateConn, productTab, "customer", query, query)
 
+		switchWritesDryRun(t, workflowType, ksWorkflow, dryRunResultsSwitchWritesCustomerShard)
+
+		testSwitchWritesErrorHandling(t, []*cluster.VttabletProcess{productTab}, []*cluster.VttabletProcess{customerTab1, customerTab2},
+			workflow, workflowType)
+
 		var commit func(t *testing.T)
 		if withOpenTx {
 			commit, _ = vc.startQuery(t, openTxQuery)
 		}
-		switchWritesDryRun(t, workflowType, ksWorkflow, dryRunResultsSwitchWritesCustomerShard)
+		// Now let's confirm that it works as expected with an error.
 		switchWrites(t, workflowType, ksWorkflow, false)
 
 		checkThatVDiffFails(t, targetKs, workflow)
@@ -998,6 +1003,7 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		require.NoError(t, vc.AddShards(t, cells, keyspace, targetShards, defaultReplicas, defaultRdonly, tabletIDBase, targetKsOpts))
 
 		tablets := vc.getVttabletsInKeyspace(t, defaultCell, ksName, "primary")
+		var sourceTablets, targetTablets []*cluster.VttabletProcess
 
 		// Test multi-primary setups, like a Galera cluster, which have auto increment steps > 1.
 		for _, tablet := range tablets {
@@ -1010,9 +1016,11 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		targetShards = "," + targetShards + ","
 		for _, tab := range tablets {
 			if strings.Contains(targetShards, ","+tab.Shard+",") {
+				targetTablets = append(targetTablets, tab)
 				log.Infof("Waiting for vrepl to catch up on %s since it IS a target shard", tab.Shard)
 				catchup(t, tab, workflow, "Reshard")
 			} else {
+				sourceTablets = append(sourceTablets, tab)
 				log.Infof("Not waiting for vrepl to catch up on %s since it is NOT a target shard", tab.Shard)
 				continue
 			}
@@ -1026,6 +1034,10 @@ func reshard(t *testing.T, ksName string, tableName string, workflow string, sou
 		if dryRunResultSwitchWrites != nil {
 			reshardAction(t, "SwitchTraffic", workflow, ksName, "", "", callNames, "primary", "--dry-run")
 		}
+		if tableName == "customer" {
+			testSwitchWritesErrorHandling(t, sourceTablets, targetTablets, workflow, "reshard")
+		}
+		// Now let's confirm that it works as expected with an error.
 		reshardAction(t, "SwitchTraffic", workflow, ksName, "", "", callNames, "primary")
 		reshardAction(t, "Complete", workflow, ksName, "", "", "", "")
 		for tabletName, count := range counts {
@@ -1534,6 +1546,140 @@ func switchWritesDryRun(t *testing.T, workflowType, ksWorkflow string, dryRunRes
 	validateDryRunResults(t, output, dryRunResults)
 }
 
+// testSwitchWritesErrorHandling confirms that switching writes works as expected
+// in the face of vreplication lag (canSwitch() precheck) and when canceling the
+// switch due to replication failing to catch up in time.
+// The workflow MUST be migrating the customer table from the source to the
+// target keyspace AND the workflow must currently have reads switched but not
+// writes.
+func testSwitchWritesErrorHandling(t *testing.T, sourceTablets, targetTablets []*cluster.VttabletProcess, workflow, workflowType string) {
+	t.Run("validate switch writes error handling", func(t *testing.T) {
+		vtgateConn := getConnection(t, vc.ClusterConfig.hostname, vc.ClusterConfig.vtgateMySQLPort)
+		defer vtgateConn.Close()
+		require.NotZero(t, len(sourceTablets), "no source tablets provided")
+		require.NotZero(t, len(targetTablets), "no target tablets provided")
+		sourceKs := sourceTablets[0].Keyspace
+		targetKs := targetTablets[0].Keyspace
+		ksWorkflow := fmt.Sprintf("%s.%s", targetKs, workflow)
+		var err error
+		sourceConns := make([]*mysql.Conn, len(sourceTablets))
+		for i, tablet := range sourceTablets {
+			sourceConns[i], err = tablet.TabletConn(tablet.Keyspace, true)
+			require.NoError(t, err)
+			defer sourceConns[i].Close()
+		}
+		targetConns := make([]*mysql.Conn, len(targetTablets))
+		for i, tablet := range targetTablets {
+			targetConns[i], err = tablet.TabletConn(tablet.Keyspace, true)
+			require.NoError(t, err)
+			defer targetConns[i].Close()
+		}
+		startingTestRowID := 10000000
+		numTestRows := 100
+		addTestRows := func() {
+			for i := 0; i < numTestRows; i++ {
+				execVtgateQuery(t, vtgateConn, sourceTablets[0].Keyspace, fmt.Sprintf("insert into customer (cid, name) values (%d, 'laggingCustomer')",
+					startingTestRowID+i))
+			}
+		}
+		deleteTestRows := func() {
+			execVtgateQuery(t, vtgateConn, sourceTablets[0].Keyspace, fmt.Sprintf("delete from customer where cid >= %d", startingTestRowID))
+		}
+		addIndex := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "set session sql_mode=''")
+				execQuery(t, targetConn, "alter table customer add unique index name_idx (name)")
+			}
+		}
+		dropIndex := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "alter table customer drop index name_idx")
+			}
+		}
+		lockTargetTable := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "lock table customer read")
+			}
+		}
+		unlockTargetTable := func() {
+			for _, targetConn := range targetConns {
+				execQuery(t, targetConn, "unlock tables")
+			}
+		}
+		cleanupTestData := func() {
+			dropIndex()
+			deleteTestRows()
+		}
+		restartWorkflow := func() {
+			err = vc.VtctldClient.ExecuteCommand("workflow", "--keyspace", targetKs, "start", "--workflow", workflow)
+			require.NoError(t, err, "failed to start workflow: %v", err)
+		}
+		waitForTargetToCatchup := func() {
+			waitForWorkflowState(t, vc, ksWorkflow, binlogdatapb.VReplicationWorkflowState_Running.String())
+			waitForNoWorkflowLag(t, vc, targetKs, workflow)
+		}
+
+		// First let's test that the prechecks work as expected. We ALTER
+		// the table on the target shards to add a unique index on the name
+		// field.
+		addIndex()
+		// Then we replicate some test rows across the target shards by
+		// inserting them in the source keyspace.
+		addTestRows()
+		// Now the workflow should go into the error state and the lag should
+		// start to climb. So we sleep for twice the max lag duration that we
+		// will set for the SwitchTraffic call.
+		lagDuration := 3 * time.Second
+		time.Sleep(lagDuration * 3)
+		out, err := vc.VtctldClient.ExecuteCommandWithOutput(workflowType, "--workflow", workflow, "--target-keyspace", targetKs,
+			"SwitchTraffic", "--tablet-types=primary", "--timeout=30s", "--max-replication-lag-allowed", lagDuration.String())
+		// It should fail in the canSwitch() precheck.
+		require.Error(t, err)
+		require.Regexp(t, fmt.Sprintf(".*cannot switch traffic for workflow %s at this time: replication lag [0-9]+s is higher than allowed lag %s.*",
+			workflow, lagDuration.String()), out)
+		require.NotContains(t, out, "cancel migration failed")
+		// Confirm that queries still work fine.
+		execVtgateQuery(t, vtgateConn, sourceKs, "select * from customer limit 1")
+		cleanupTestData()
+		// We have to restart the workflow again as the duplicate key error
+		// is a permanent/terminal one.
+		restartWorkflow()
+		waitForTargetToCatchup()
+
+		// Now let's test that the cancel works by setting the command timeout
+		// to a fraction (6s) of the default max repl lag duration (30s). First
+		// we lock the customer table on the target tablets so that we cannot
+		// apply the INSERTs and catch up.
+		lockTargetTable()
+		addTestRows()
+		timeout := lagDuration * 2 // 6s
+		// Use the default max-replication-lag-allowed value of 30s.
+		// We run the command in a goroutine so that we can unblock things
+		// after the timeout is reached -- as the vplayer query is blocking
+		// on the table lock in the MySQL layer.
+		wg := sync.WaitGroup{}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			out, err = vc.VtctldClient.ExecuteCommandWithOutput(workflowType, "--workflow", workflow, "--target-keyspace", targetKs,
+				"SwitchTraffic", "--tablet-types=primary", "--timeout", timeout.String())
+		}()
+		time.Sleep(timeout)
+		// Now we can unblock things and let it continue.
+		unlockTargetTable()
+		wg.Wait()
+		// It should fail due to the command context timeout and we should
+		// successfully cancel.
+		require.Error(t, err)
+		require.Contains(t, out, "failed to sync up replication between the source and target")
+		require.NotContains(t, out, "cancel migration failed")
+		// Confirm that queries still work fine.
+		execVtgateQuery(t, vtgateConn, sourceKs, "select * from customer limit 1")
+		deleteTestRows()
+		waitForTargetToCatchup()
+	})
+}
+
 // restartWorkflow confirms that a workflow can be successfully
 // stopped and started.
 func restartWorkflow(t *testing.T, ksWorkflow string) {