// SetBlacklistedTablesByShard sets the blacklisted table list of all
// tablets of a given type in a shard. It would work for the master,
// but it wouldn't be very efficient.
func (wr *Wrangler) SetBlacklistedTablesByShard(keyspace, shard string, tabletType topo.TabletType, tables []string) error {
	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	switch err {
	case nil:
		// keep going
	case topo.ErrPartialResult:
		log.Warningf("SetBlacklistedTablesByShard: got partial result, may not blacklist everything everywhere")
	default:
		return err
	}

	// ignore errors in this phase
	wg := sync.WaitGroup{}
	for _, ti := range tabletMap {
		if ti.Type != tabletType {
			continue
		}

		wg.Add(1)
		go func(ti *topo.TabletInfo) {
			if err := wr.ai.SetBlacklistedTables(ti, tables, wr.ActionTimeout()); err != nil {
				log.Warningf("SetBlacklistedTablesByShard: failed to set tables for %v: %v", ti.Alias, err)
			}
			wg.Done()
		}(ti)
	}
	wg.Wait()

	return nil
}

func (wr *Wrangler) reparentShardLocked(keyspace, shard string, masterElectTabletAlias topo.TabletAlias, leaveMasterReadOnly, forceReparentToCurrentMaster bool) error {
	// critical read, we want up to date info (and the shard is locked).
	shardInfo, err := wr.ts.GetShardCritical(keyspace, shard)
	if err != nil {
		return err
	}

	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	if err != nil {
		return err
	}

	slaveTabletMap, masterTabletMap := sortedTabletMap(tabletMap)
	if shardInfo.MasterAlias == masterElectTabletAlias && !forceReparentToCurrentMaster {
		return fmt.Errorf("master-elect tablet %v is already master - specify -force to override", masterElectTabletAlias)
	}

	masterElectTablet, ok := tabletMap[masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v not found in replication graph %v/%v %v", masterElectTabletAlias, keyspace, shard, mapKeys(tabletMap))
	}

	if !shardInfo.MasterAlias.IsZero() && !forceReparentToCurrentMaster {
		err = wr.reparentShardGraceful(shardInfo, slaveTabletMap, masterTabletMap, masterElectTablet, leaveMasterReadOnly)
	} else {
		err = wr.reparentShardBrutal(shardInfo, slaveTabletMap, masterTabletMap, masterElectTablet, leaveMasterReadOnly, forceReparentToCurrentMaster)
	}
	if err == nil {
		// only log if it works, if it fails we'll show the error
		log.Infof("reparentShard finished")
	}
	return err
}

func (wr *Wrangler) shardExternallyReparentedLocked(keyspace, shard string, masterElectTabletAlias topo.TabletAlias) error {
	// read the shard, make sure the master is not already good.
	// critical read, we want up to date info (and the shard is locked).
	shardInfo, err := wr.ts.GetShardCritical(keyspace, shard)
	if err != nil {
		return err
	}
	if shardInfo.MasterAlias == masterElectTabletAlias {
		return fmt.Errorf("master-elect tablet %v is already master", masterElectTabletAlias)
	}

	// Read the tablets, make sure the master elect is known to us.
	// Note we will keep going with a partial tablet map, which usually
	// happens when a cell is not reachable. After these checks, the
	// guarantees we'll have are:
	// - global cell is reachable (we just locked and read the shard)
	// - the local cell that contains the new master is reachable
	//   (as we're going to check the new master is in the list)
	// That should be enough.
	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	switch err {
	case nil:
		// keep going
	case topo.ErrPartialResult:
		log.Warningf("Got topo.ErrPartialResult from GetTabletMapForShard, may need to re-init some tablets")
	default:
		return err
	}
	masterElectTablet, ok := tabletMap[masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v not found in replication graph %v/%v %v", masterElectTabletAlias, keyspace, shard, mapKeys(tabletMap))
	}

	// sort the tablets, and handle them
	slaveTabletMap, masterTabletMap := sortedTabletMap(tabletMap)
	err = wr.reparentShardExternal(slaveTabletMap, masterTabletMap, masterElectTablet)
	if err != nil {
		log.Infof("Skipping shard rebuild with failed reparent")
		return err
	}

	// Compute the list of Cells we need to rebuild: old master and
	// new master cells.
	cells := []string{shardInfo.MasterAlias.Cell}
	if shardInfo.MasterAlias.Cell != masterElectTabletAlias.Cell {
		cells = append(cells, masterElectTabletAlias.Cell)
	}

	// now update the master record in the shard object
	log.Infof("Updating Shard's MasterAlias record")
	shardInfo.MasterAlias = masterElectTabletAlias
	if err = wr.ts.UpdateShard(shardInfo); err != nil {
		return err
	}

	// and rebuild the shard serving graph
	log.Infof("Rebuilding shard serving graph data")
	return topotools.RebuildShard(wr.ts, masterElectTablet.Keyspace, masterElectTablet.Shard, cells, wr.lockTimeout, interrupted)
}

func (wr *Wrangler) shardReplicationStatuses(shardInfo *topo.ShardInfo) ([]*topo.TabletInfo, []*myproto.ReplicationStatus, error) {
	// FIXME(msolomon) this assumes no hierarchical replication, which is currently the case.
	tabletMap, err := topo.GetTabletMapForShard(wr.ts, shardInfo.Keyspace(), shardInfo.ShardName())
	if err != nil {
		return nil, nil, err
	}
	tablets := topotools.CopyMapValues(tabletMap, []*topo.TabletInfo{}).([]*topo.TabletInfo)
	stats, err := wr.tabletReplicationStatuses(tablets)
	return tablets, stats, err
}

// DeleteShard will do all the necessary changes in the topology server
// to entirely remove a shard.
func (wr *Wrangler) DeleteShard(ctx context.Context, keyspace, shard string, recursive bool) error {
	shardInfo, err := wr.ts.GetShard(ctx, keyspace, shard)
	if err != nil {
		return err
	}

	tabletMap, err := topo.GetTabletMapForShard(ctx, wr.ts, keyspace, shard)
	if err != nil {
		return err
	}
	if recursive {
		wr.Logger().Infof("Deleting all tablets in shard %v/%v", keyspace, shard)
		for tabletAlias := range tabletMap {
			// We don't care about scrapping or updating the replication graph,
			// because we're about to delete the entire replication graph.
			wr.Logger().Infof("Deleting tablet %v", tabletAlias)
			if err := wr.TopoServer().DeleteTablet(ctx, tabletAlias); err != nil && err != topo.ErrNoNode {
				// Unlike the errors below in non-recursive steps, we don't want to
				// continue if a DeleteTablet fails. If we continue and delete the
				// replication graph, the tablet record will be orphaned, since we'll
				// no longer know it belongs to this shard.
				//
				// If the problem is temporary, or resolved externally, re-running
				// DeleteShard will skip over tablets that were already deleted.
				return fmt.Errorf("can't delete tablet %v: %v", tabletAlias, err)
			}
		}
	} else if len(tabletMap) > 0 {
		return fmt.Errorf("shard %v/%v still has %v tablets; use -recursive or remove them manually", keyspace, shard, len(tabletMap))
	}

	// remove the replication graph and serving graph in each cell
	for _, cell := range shardInfo.Cells {
		if err := wr.ts.DeleteShardReplication(ctx, cell, keyspace, shard); err != nil && err != topo.ErrNoNode {
			wr.Logger().Warningf("Cannot delete ShardReplication in cell %v for %v/%v: %v", cell, keyspace, shard, err)
		}

		for _, t := range topo.AllTabletTypes {
			if !topo.IsInServingGraph(t) {
				continue
			}

			if err := wr.ts.DeleteEndPoints(ctx, cell, keyspace, shard, t, -1); err != nil && err != topo.ErrNoNode {
				wr.Logger().Warningf("Cannot delete EndPoints in cell %v for %v/%v/%v: %v", cell, keyspace, shard, t, err)
			}
		}

		if err := wr.ts.DeleteSrvShard(ctx, cell, keyspace, shard); err != nil && err != topo.ErrNoNode {
			wr.Logger().Warningf("Cannot delete SrvShard in cell %v for %v/%v: %v", cell, keyspace, shard, err)
		}
	}

	return wr.ts.DeleteShard(ctx, keyspace, shard)
}

func (wr *Wrangler) reparentShardLocked(keyspace, shard string, masterElectTabletAlias topo.TabletAlias, leaveMasterReadOnly, forceReparentToCurrentMaster bool) error {
	shardInfo, err := wr.ts.GetShard(keyspace, shard)
	if err != nil {
		return err
	}

	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	if err != nil {
		return err
	}

	slaveTabletMap, masterTabletMap := topotools.SortedTabletMap(tabletMap)
	if shardInfo.MasterAlias == masterElectTabletAlias && !forceReparentToCurrentMaster {
		return fmt.Errorf("master-elect tablet %v is already master - specify -force to override", masterElectTabletAlias)
	}

	masterElectTablet, ok := tabletMap[masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v not found in replication graph %v/%v %v", masterElectTabletAlias, keyspace, shard, topotools.MapKeys(tabletMap))
	}

	// Create reusable Reparent event with available info
	ev := &events.Reparent{
		ShardInfo: *shardInfo,
		NewMaster: *masterElectTablet.Tablet,
	}

	if oldMasterTablet, ok := tabletMap[shardInfo.MasterAlias]; ok {
		ev.OldMaster = *oldMasterTablet.Tablet
	}

	if !shardInfo.MasterAlias.IsZero() && !forceReparentToCurrentMaster {
		err = wr.reparentShardGraceful(ev, shardInfo, slaveTabletMap, masterTabletMap, masterElectTablet, leaveMasterReadOnly)
	} else {
		err = wr.reparentShardBrutal(ev, shardInfo, slaveTabletMap, masterTabletMap, masterElectTablet, leaveMasterReadOnly, forceReparentToCurrentMaster)
	}

	if err == nil {
		// only log if it works, if it fails we'll show the error
		wr.Logger().Infof("reparentShard finished")
	}
	return err
}

// DeleteShard will do all the necessary changes in the topology server
// to entirely remove a shard. It can only work if there are no tablets
// in that shard.
func (wr *Wrangler) DeleteShard(keyspace, shard string) error {
	shardInfo, err := wr.ts.GetShard(keyspace, shard)
	if err != nil {
		return err
	}

	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	if err != nil {
		return err
	}
	if len(tabletMap) > 0 {
		return fmt.Errorf("shard %v/%v still has %v tablets", keyspace, shard, len(tabletMap))
	}

	// remove the replication graph and serving graph in each cell
	for _, cell := range shardInfo.Cells {
		if err := wr.ts.DeleteShardReplication(cell, keyspace, shard); err != nil {
			log.Warningf("Cannot delete ShardReplication in cell %v for %v/%v: %v", cell, keyspace, shard, err)
		}

		for _, t := range topo.AllTabletTypes {
			if !topo.IsInServingGraph(t) {
				continue
			}

			if err := wr.ts.DeleteEndPoints(cell, keyspace, shard, t); err != nil && err != topo.ErrNoNode {
				log.Warningf("Cannot delete EndPoints in cell %v for %v/%v/%v: %v", cell, keyspace, shard, t, err)
			}
		}

		if err := wr.ts.DeleteSrvShard(cell, keyspace, shard); err != nil && err != topo.ErrNoNode {
			log.Warningf("Cannot delete SrvShard in cell %v for %v/%v: %v", cell, keyspace, shard, err)
		}
	}

	return wr.ts.DeleteShard(keyspace, shard)
}

func TestShardExternallyReparented(t *testing.T) {
	ts := zktopo.NewTestServer(t, []string{"cell1", "cell2"})
	wr := wrangler.New(logutil.NewConsoleLogger(), ts, time.Minute, time.Second)
	wr.UseRPCs = false

	// Create an old master, a new master, two good slaves, one bad slave
	oldMaster := NewFakeTablet(t, wr, "cell1", 0, topo.TYPE_MASTER)
	newMaster := NewFakeTablet(t, wr, "cell1", 1, topo.TYPE_REPLICA,
		TabletParent(oldMaster.Tablet.Alias))
	goodSlave1 := NewFakeTablet(t, wr, "cell1", 2, topo.TYPE_REPLICA,
		TabletParent(oldMaster.Tablet.Alias))
	goodSlave2 := NewFakeTablet(t, wr, "cell2", 3, topo.TYPE_REPLICA,
		TabletParent(oldMaster.Tablet.Alias))
	badSlave := NewFakeTablet(t, wr, "cell1", 4, topo.TYPE_REPLICA,
		TabletParent(oldMaster.Tablet.Alias))

	// Add a new Cell to the Shard, that doesn't map to any read topo cell,
	// to simulate a data center being unreachable.
	si, err := ts.GetShard("test_keyspace", "0")
	if err != nil {
		t.Fatalf("GetShard failed: %v", err)
	}
	si.Cells = append(si.Cells, "cell666")
	if err := topo.UpdateShard(ts, si); err != nil {
		t.Fatalf("UpdateShard failed: %v", err)
	}

	// Slightly unrelated test: make sure we can find the tablets
	// even with a datacenter being down.
	tabletMap, err := topo.GetTabletMapForShardByCell(ts, "test_keyspace", "0", []string{"cell1"})
	if err != nil {
		t.Fatalf("GetTabletMapForShardByCell should have worked but got: %v", err)
	}
	master, err := topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != nil || master != oldMaster.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(master) failed: %v %v", err, master)
	}
	slave1, err := topotools.FindTabletByIPAddrAndPort(tabletMap, goodSlave1.Tablet.IPAddr, "vt", goodSlave1.Tablet.Portmap["vt"])
	if err != nil || slave1 != goodSlave1.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(slave1) failed: %v %v", err, master)
	}
	slave2, err := topotools.FindTabletByIPAddrAndPort(tabletMap, goodSlave2.Tablet.IPAddr, "vt", goodSlave2.Tablet.Portmap["vt"])
	if err != topo.ErrNoNode {
		t.Fatalf("FindTabletByIPAddrAndPort(slave2) worked: %v %v", err, slave2)
	}

	// Make sure the master is not exported in other cells
	tabletMap, err = topo.GetTabletMapForShardByCell(ts, "test_keyspace", "0", []string{"cell2"})
	master, err = topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != topo.ErrNoNode {
		t.Fatalf("FindTabletByIPAddrAndPort(master) worked in cell2: %v %v", err, master)
	}

	tabletMap, err = topo.GetTabletMapForShard(ts, "test_keyspace", "0")
	if err != topo.ErrPartialResult {
		t.Fatalf("GetTabletMapForShard should have returned ErrPartialResult but got: %v", err)
	}
	master, err = topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != nil || master != oldMaster.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(master) failed: %v %v", err, master)
	}

	// First test: reparent to the same master, make sure it works
	// as expected.
	if err := wr.ShardExternallyReparented("test_keyspace", "0", oldMaster.Tablet.Alias); err == nil {
		t.Fatalf("ShardExternallyReparented(same master) should have failed")
	} else {
		if !strings.Contains(err.Error(), "already master") {
			t.Fatalf("ShardExternallyReparented(same master) should have failed with an error that contains 'already master' but got: %v", err)
		}
	}

	// Second test: reparent to the replica, and pretend the old
	// master is still good to go.

	// On the elected master, we will respond to
	// TABLET_ACTION_SLAVE_WAS_PROMOTED
	newMaster.FakeMysqlDaemon.MasterAddr = ""
	newMaster.StartActionLoop(t, wr)
	defer newMaster.StopActionLoop(t)

	// On the old master, we will only respond to
	// TABLET_ACTION_SLAVE_WAS_RESTARTED.
	oldMaster.FakeMysqlDaemon.MasterAddr = newMaster.Tablet.MysqlIpAddr()
	oldMaster.StartActionLoop(t, wr)
	defer oldMaster.StopActionLoop(t)

	// On the good slaves, we will respond to
	// TABLET_ACTION_SLAVE_WAS_RESTARTED.
	goodSlave1.FakeMysqlDaemon.MasterAddr = newMaster.Tablet.MysqlIpAddr()
	goodSlave1.StartActionLoop(t, wr)
	defer goodSlave1.StopActionLoop(t)

	goodSlave2.FakeMysqlDaemon.MasterAddr = newMaster.Tablet.MysqlIpAddr()
	goodSlave2.StartActionLoop(t, wr)
	defer goodSlave2.StopActionLoop(t)

	// On the bad slave, we will respond to
	// TABLET_ACTION_SLAVE_WAS_RESTARTED with bad data.
	badSlave.FakeMysqlDaemon.MasterAddr = "234.0.0.1:3301"
//.........这里部分代码省略.........

func (wr *Wrangler) applySchemaShardComplex(statusArray []*TabletStatus, shardInfo *topo.ShardInfo, preflight *myproto.SchemaChangeResult, masterTabletAlias topo.TabletAlias, change string, newParentTabletAlias topo.TabletAlias, force bool) (*myproto.SchemaChangeResult, error) {
	// apply the schema change to all replica / slave tablets
	for _, status := range statusArray {
		// if already applied, we skip this guy
		diffs := myproto.DiffSchemaToArray("after", preflight.AfterSchema, status.ti.Alias.String(), status.beforeSchema)
		if len(diffs) == 0 {
			log.Infof("Tablet %v already has the AfterSchema, skipping", status.ti.Alias)
			continue
		}

		// make sure the before schema matches
		diffs = myproto.DiffSchemaToArray("master", preflight.BeforeSchema, status.ti.Alias.String(), status.beforeSchema)
		if len(diffs) > 0 {
			if force {
				log.Warningf("Tablet %v has inconsistent schema, ignoring: %v", status.ti.Alias, strings.Join(diffs, "\n"))
			} else {
				return nil, fmt.Errorf("Tablet %v has inconsistent schema: %v", status.ti.Alias, strings.Join(diffs, "\n"))
			}
		}

		// take this guy out of the serving graph if necessary
		ti, err := wr.ts.GetTablet(status.ti.Alias)
		if err != nil {
			return nil, err
		}
		typeChangeRequired := ti.Tablet.IsInServingGraph()
		if typeChangeRequired {
			// note we want to update the serving graph there
			err = wr.changeTypeInternal(ti.Alias, topo.TYPE_SCHEMA_UPGRADE)
			if err != nil {
				return nil, err
			}
		}

		// apply the schema change
		log.Infof("Applying schema change to slave %v in complex mode", status.ti.Alias)
		sc := &myproto.SchemaChange{Sql: change, Force: force, AllowReplication: false, BeforeSchema: preflight.BeforeSchema, AfterSchema: preflight.AfterSchema}
		_, err = wr.ApplySchema(status.ti.Alias, sc)
		if err != nil {
			return nil, err
		}

		// put this guy back into the serving graph
		if typeChangeRequired {
			err = wr.changeTypeInternal(ti.Alias, ti.Tablet.Type)
			if err != nil {
				return nil, err
			}
		}
	}

	// if newParentTabletAlias is passed in, use that as the new master
	if !newParentTabletAlias.IsZero() {
		log.Infof("Reparenting with new master set to %v", newParentTabletAlias)
		tabletMap, err := topo.GetTabletMapForShard(wr.ts, shardInfo.Keyspace(), shardInfo.ShardName())
		if err != nil {
			return nil, err
		}

		slaveTabletMap, masterTabletMap := sortedTabletMap(tabletMap)
		newMasterTablet, err := wr.ts.GetTablet(newParentTabletAlias)
		if err != nil {
			return nil, err
		}

		err = wr.reparentShardGraceful(shardInfo, slaveTabletMap, masterTabletMap, newMasterTablet /*leaveMasterReadOnly*/, false)
		if err != nil {
			return nil, err
		}

		// Here we would apply the schema change to the old
		// master, but after a reparent it's in Scrap state,
		// so no need to.  When/if reparent leaves the
		// original master in a different state (like replica
		// or rdonly), then we should apply the schema there
		// too.
		log.Infof("Skipping schema change on old master %v in complex mode, it's been Scrapped", masterTabletAlias)
	}
	return &myproto.SchemaChangeResult{BeforeSchema: preflight.BeforeSchema, AfterSchema: preflight.AfterSchema}, nil
}

func tabletExternallyReparentedLocked(ts topo.Server, tablet *topo.TabletInfo, actionTimeout, lockTimeout time.Duration, interrupted chan struct{}) (err error) {
	// read the shard, make sure again the master is not already good.
	// critical read, we want up to date info (and the shard is locked).
	shardInfo, err := ts.GetShardCritical(tablet.Keyspace, tablet.Shard)
	if err != nil {
		return err
	}
	if shardInfo.MasterAlias == tablet.Alias {
		return fmt.Errorf("this tablet is already the master")
	}

	// Read the tablets, make sure the master elect is known to the shard
	// (it's this tablet, so it better be!).
	// Note we will keep going with a partial tablet map, which usually
	// happens when a cell is not reachable. After these checks, the
	// guarantees we'll have are:
	// - global cell is reachable (we just locked and read the shard)
	// - the local cell that contains the new master is reachable
	//   (as we're going to check the new master is in the list)
	// That should be enough.
	tabletMap, err := topo.GetTabletMapForShard(ts, tablet.Keyspace, tablet.Shard)
	switch err {
	case nil:
		// keep going
	case topo.ErrPartialResult:
		log.Warningf("Got topo.ErrPartialResult from GetTabletMapForShard, may need to re-init some tablets")
	default:
		return err
	}
	masterElectTablet, ok := tabletMap[tablet.Alias]
	if !ok {
		return fmt.Errorf("this master-elect tablet %v not found in replication graph %v/%v %v", tablet.Alias, tablet.Keyspace, tablet.Shard, topotools.MapKeys(tabletMap))
	}

	// Create reusable Reparent event with available info
	ev := &events.Reparent{
		ShardInfo: *shardInfo,
		NewMaster: *tablet.Tablet,
	}

	if oldMasterTablet, ok := tabletMap[shardInfo.MasterAlias]; ok {
		ev.OldMaster = *oldMasterTablet.Tablet
	}

	defer func() {
		if err != nil {
			event.DispatchUpdate(ev, "failed: "+err.Error())
		}
	}()

	// sort the tablets, and handle them
	slaveTabletMap, masterTabletMap := topotools.SortedTabletMap(tabletMap)
	event.DispatchUpdate(ev, "starting external from tablet")

	// we fix the new master in the replication graph
	event.DispatchUpdate(ev, "mark ourself as new master")
	err = updateReplicationGraphForPromotedSlave(ts, tablet)
	if err != nil {
		// This suggests we can't talk to topo server. This is bad.
		return fmt.Errorf("updateReplicationGraphForPromotedSlave failed: %v", err)
	}

	// Once this tablet is promoted, remove it from our maps
	delete(slaveTabletMap, tablet.Alias)
	delete(masterTabletMap, tablet.Alias)

	// Then fix all the slaves, including the old master.  This
	// last step is very likely to time out for some tablets (one
	// random guy is dead, the old master is dead, ...). We
	// execute them all in parallel until we get to
	// wr.ActionTimeout(). After this, no other action with a
	// timeout is executed, so even if we got to the timeout,
	// we're still good.
	event.DispatchUpdate(ev, "restarting slaves")
	logger := logutil.NewConsoleLogger()
	ai := initiator.NewActionInitiator(ts)
	topotools.RestartSlavesExternal(ts, logger, slaveTabletMap, masterTabletMap, masterElectTablet.Alias, func(ti *topo.TabletInfo, swrd *actionnode.SlaveWasRestartedArgs) error {
		return ai.RpcSlaveWasRestarted(ti, swrd, actionTimeout)
	})

	// Compute the list of Cells we need to rebuild: old master and
	// all other cells if reparenting to another cell.
	cells := []string{shardInfo.MasterAlias.Cell}
	if shardInfo.MasterAlias.Cell != tablet.Alias.Cell {
		cells = nil
	}

	// now update the master record in the shard object
	event.DispatchUpdate(ev, "updating shard record")
	log.Infof("Updating Shard's MasterAlias record")
	shardInfo.MasterAlias = tablet.Alias
	if err = topo.UpdateShard(ts, shardInfo); err != nil {
		return err
	}

	// and rebuild the shard serving graph
	event.DispatchUpdate(ev, "rebuilding shard serving graph")
	log.Infof("Rebuilding shard serving graph data")
	if err = topotools.RebuildShard(logger, ts, tablet.Keyspace, tablet.Shard, cells, lockTimeout, interrupted); err != nil {
		return err
//.........这里部分代码省略.........

func (wr *Wrangler) shardExternallyReparentedLocked(keyspace, shard string, masterElectTabletAlias topo.TabletAlias) (err error) {
	// read the shard, make sure the master is not already good.
	shardInfo, err := wr.ts.GetShard(keyspace, shard)
	if err != nil {
		return err
	}
	if shardInfo.MasterAlias == masterElectTabletAlias {
		return fmt.Errorf("master-elect tablet %v is already master", masterElectTabletAlias)
	}

	// Read the tablets, make sure the master elect is known to us.
	// Note we will keep going with a partial tablet map, which usually
	// happens when a cell is not reachable. After these checks, the
	// guarantees we'll have are:
	// - global cell is reachable (we just locked and read the shard)
	// - the local cell that contains the new master is reachable
	//   (as we're going to check the new master is in the list)
	// That should be enough.
	tabletMap, err := topo.GetTabletMapForShard(wr.ts, keyspace, shard)
	switch err {
	case nil:
		// keep going
	case topo.ErrPartialResult:
		wr.logger.Warningf("Got topo.ErrPartialResult from GetTabletMapForShard, may need to re-init some tablets")
	default:
		return err
	}
	masterElectTablet, ok := tabletMap[masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v not found in replication graph %v/%v %v", masterElectTabletAlias, keyspace, shard, topotools.MapKeys(tabletMap))
	}

	// Create reusable Reparent event with available info
	ev := &events.Reparent{
		ShardInfo: *shardInfo,
		NewMaster: *masterElectTablet.Tablet,
	}

	if oldMasterTablet, ok := tabletMap[shardInfo.MasterAlias]; ok {
		ev.OldMaster = *oldMasterTablet.Tablet
	}

	defer func() {
		if err != nil {
			event.DispatchUpdate(ev, "failed: "+err.Error())
		}
	}()

	// sort the tablets, and handle them
	slaveTabletMap, masterTabletMap := topotools.SortedTabletMap(tabletMap)
	err = wr.reparentShardExternal(ev, slaveTabletMap, masterTabletMap, masterElectTablet)
	if err != nil {
		wr.logger.Infof("Skipping shard rebuild with failed reparent")
		return err
	}

	// Compute the list of Cells we need to rebuild: old master and
	// all other cells if reparenting to another cell.
	cells := []string{shardInfo.MasterAlias.Cell}
	if shardInfo.MasterAlias.Cell != masterElectTabletAlias.Cell {
		cells = nil
	}

	// now update the master record in the shard object
	event.DispatchUpdate(ev, "updating shard record")
	wr.logger.Infof("Updating Shard's MasterAlias record")
	shardInfo.MasterAlias = masterElectTabletAlias
	if err = topo.UpdateShard(wr.ts, shardInfo); err != nil {
		return err
	}

	// and rebuild the shard serving graph
	event.DispatchUpdate(ev, "rebuilding shard serving graph")
	wr.logger.Infof("Rebuilding shard serving graph data")
	if _, err = topotools.RebuildShard(wr.logger, wr.ts, masterElectTablet.Keyspace, masterElectTablet.Shard, cells, wr.lockTimeout, interrupted); err != nil {
		return err
	}

	event.DispatchUpdate(ev, "finished")
	return nil
}

func TestTabletExternallyReparented(t *testing.T) {
	tabletmanager.SetReparentFlags(time.Minute /* finalizeTimeout */)

	ctx := context.Background()
	ts := zktopo.NewTestServer(t, []string{"cell1", "cell2"})
	wr := wrangler.New(logutil.NewConsoleLogger(), ts, tmclient.NewTabletManagerClient(), time.Second)
	vp := NewVtctlPipe(t, ts)
	defer vp.Close()

	// Create an old master, a new master, two good slaves, one bad slave
	oldMaster := NewFakeTablet(t, wr, "cell1", 0, topo.TYPE_MASTER)
	newMaster := NewFakeTablet(t, wr, "cell1", 1, topo.TYPE_REPLICA)
	goodSlave1 := NewFakeTablet(t, wr, "cell1", 2, topo.TYPE_REPLICA)
	goodSlave2 := NewFakeTablet(t, wr, "cell2", 3, topo.TYPE_REPLICA)
	badSlave := NewFakeTablet(t, wr, "cell1", 4, topo.TYPE_REPLICA)

	// Add a new Cell to the Shard, that doesn't map to any read topo cell,
	// to simulate a data center being unreachable.
	si, err := ts.GetShard(ctx, "test_keyspace", "0")
	if err != nil {
		t.Fatalf("GetShard failed: %v", err)
	}
	si.Cells = append(si.Cells, "cell666")
	if err := topo.UpdateShard(ctx, ts, si); err != nil {
		t.Fatalf("UpdateShard failed: %v", err)
	}

	// Slightly unrelated test: make sure we can find the tablets
	// even with a datacenter being down.
	tabletMap, err := topo.GetTabletMapForShardByCell(ctx, ts, "test_keyspace", "0", []string{"cell1"})
	if err != nil {
		t.Fatalf("GetTabletMapForShardByCell should have worked but got: %v", err)
	}
	master, err := topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != nil || master != oldMaster.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(master) failed: %v %v", err, master)
	}
	slave1, err := topotools.FindTabletByIPAddrAndPort(tabletMap, goodSlave1.Tablet.IPAddr, "vt", goodSlave1.Tablet.Portmap["vt"])
	if err != nil || slave1 != goodSlave1.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(slave1) failed: %v %v", err, master)
	}
	slave2, err := topotools.FindTabletByIPAddrAndPort(tabletMap, goodSlave2.Tablet.IPAddr, "vt", goodSlave2.Tablet.Portmap["vt"])
	if err != topo.ErrNoNode {
		t.Fatalf("FindTabletByIPAddrAndPort(slave2) worked: %v %v", err, slave2)
	}

	// Make sure the master is not exported in other cells
	tabletMap, err = topo.GetTabletMapForShardByCell(ctx, ts, "test_keyspace", "0", []string{"cell2"})
	master, err = topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != topo.ErrNoNode {
		t.Fatalf("FindTabletByIPAddrAndPort(master) worked in cell2: %v %v", err, master)
	}

	tabletMap, err = topo.GetTabletMapForShard(ctx, ts, "test_keyspace", "0")
	if err != topo.ErrPartialResult {
		t.Fatalf("GetTabletMapForShard should have returned ErrPartialResult but got: %v", err)
	}
	master, err = topotools.FindTabletByIPAddrAndPort(tabletMap, oldMaster.Tablet.IPAddr, "vt", oldMaster.Tablet.Portmap["vt"])
	if err != nil || master != oldMaster.Tablet.Alias {
		t.Fatalf("FindTabletByIPAddrAndPort(master) failed: %v %v", err, master)
	}

	// On the elected master, we will respond to
	// TabletActionSlaveWasPromoted
	newMaster.StartActionLoop(t, wr)
	defer newMaster.StopActionLoop(t)

	// On the old master, we will only respond to
	// TabletActionSlaveWasRestarted.
	oldMaster.StartActionLoop(t, wr)
	defer oldMaster.StopActionLoop(t)

	// On the good slaves, we will respond to
	// TabletActionSlaveWasRestarted.
	goodSlave1.StartActionLoop(t, wr)
	defer goodSlave1.StopActionLoop(t)

	goodSlave2.StartActionLoop(t, wr)
	defer goodSlave2.StopActionLoop(t)

	// On the bad slave, we will respond to
	// TabletActionSlaveWasRestarted with bad data.
	badSlave.StartActionLoop(t, wr)
	defer badSlave.StopActionLoop(t)

	// First test: reparent to the same master, make sure it works
	// as expected.
	tmc := tmclient.NewTabletManagerClient()
	ti, err := ts.GetTablet(ctx, oldMaster.Tablet.Alias)
	if err != nil {
		t.Fatalf("GetTablet failed: %v", err)
	}
	if err := vp.Run([]string{"TabletExternallyReparented", oldMaster.Tablet.Alias.String()}); err != nil {
		t.Fatalf("TabletExternallyReparented(same master) should have worked")
	}

	// Second test: reparent to a replica, and pretend the old
	// master is still good to go.

	// This tests a bad case; the new designated master is a slave,
//.........这里部分代码省略.........

func (wr *Wrangler) emergencyReparentShardLocked(ctx context.Context, ev *events.Reparent, keyspace, shard string, masterElectTabletAlias *pb.TabletAlias, waitSlaveTimeout time.Duration) error {
	shardInfo, err := wr.ts.GetShard(ctx, keyspace, shard)
	if err != nil {
		return err
	}
	ev.ShardInfo = *shardInfo

	event.DispatchUpdate(ev, "reading all tablets")
	tabletMap, err := topo.GetTabletMapForShard(ctx, wr.ts, keyspace, shard)
	if err != nil {
		return err
	}

	// Check corner cases we're going to depend on
	masterElectTabletInfo, ok := tabletMap[*masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v is not in the shard", masterElectTabletAlias)
	}
	ev.NewMaster = *masterElectTabletInfo.Tablet
	if topo.TabletAliasEqual(shardInfo.MasterAlias, masterElectTabletAlias) {
		return fmt.Errorf("master-elect tablet %v is already the master", masterElectTabletAlias)
	}

	// Deal with the old master: try to remote-scrap it, if it's
	// truely dead we force-scrap it. Remove it from our map in any case.
	if !topo.TabletAliasIsZero(shardInfo.MasterAlias) {
		scrapOldMaster := true
		oldMasterTabletInfo, ok := tabletMap[*shardInfo.MasterAlias]
		if ok {
			delete(tabletMap, *shardInfo.MasterAlias)
		} else {
			oldMasterTabletInfo, err = wr.ts.GetTablet(ctx, shardInfo.MasterAlias)
			if err != nil {
				wr.logger.Warningf("cannot read old master tablet %v, won't touch it: %v", shardInfo.MasterAlias, err)
				scrapOldMaster = false
			}
		}

		if scrapOldMaster {
			ev.OldMaster = *oldMasterTabletInfo.Tablet
			wr.logger.Infof("scrapping old master %v", shardInfo.MasterAlias)

			ctx, cancel := context.WithTimeout(ctx, waitSlaveTimeout)
			defer cancel()

			if err := wr.tmc.Scrap(ctx, oldMasterTabletInfo); err != nil {
				wr.logger.Warningf("remote scrapping failed master failed, will force the scrap: %v", err)

				if err := topotools.Scrap(ctx, wr.ts, shardInfo.MasterAlias, true); err != nil {
					wr.logger.Warningf("old master topo scrapping failed, continuing anyway: %v", err)
				}
			}
		}
	}

	// Stop replication on all slaves, get their current
	// replication position
	event.DispatchUpdate(ev, "stop replication on all slaves")
	wg := sync.WaitGroup{}
	mu := sync.Mutex{}
	statusMap := make(map[pb.TabletAlias]myproto.ReplicationStatus)
	for alias, tabletInfo := range tabletMap {
		wg.Add(1)
		go func(alias pb.TabletAlias, tabletInfo *topo.TabletInfo) {
			defer wg.Done()
			wr.logger.Infof("getting replication position from %v", alias)
			ctx, cancel := context.WithTimeout(ctx, waitSlaveTimeout)
			defer cancel()
			rp, err := wr.TabletManagerClient().StopReplicationAndGetStatus(ctx, tabletInfo)
			if err != nil {
				wr.logger.Warningf("failed to get replication status from %v, ignoring tablet: %v", alias, err)
				return
			}
			mu.Lock()
			statusMap[alias] = rp
			mu.Unlock()
		}(alias, tabletInfo)
	}
	wg.Wait()

	// Verify masterElect is alive and has the most advanced position
	masterElectStatus, ok := statusMap[*masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("couldn't get master elect %v replication position", masterElectTabletAlias)
	}
	for alias, status := range statusMap {
		if topo.TabletAliasEqual(&alias, masterElectTabletAlias) {
			continue
		}
		if !masterElectStatus.Position.AtLeast(status.Position) {
			return fmt.Errorf("tablet %v is more advanced than master elect tablet %v: %v > %v", alias, masterElectTabletAlias, status.Position, masterElectStatus)
		}
	}

	// Promote the masterElect
	wr.logger.Infof("promote slave %v", masterElectTabletAlias)
	event.DispatchUpdate(ev, "promoting slave")
	rp, err := wr.tmc.PromoteSlave(ctx, masterElectTabletInfo)
	if err != nil {
		return fmt.Errorf("master-elect tablet %v failed to be upgraded to master: %v", masterElectTabletAlias, err)
//.........这里部分代码省略.........

func (wr *Wrangler) plannedReparentShardLocked(ctx context.Context, ev *events.Reparent, keyspace, shard string, masterElectTabletAlias *pb.TabletAlias, waitSlaveTimeout time.Duration) error {
	shardInfo, err := wr.ts.GetShard(ctx, keyspace, shard)
	if err != nil {
		return err
	}
	ev.ShardInfo = *shardInfo

	event.DispatchUpdate(ev, "reading tablet map")
	tabletMap, err := topo.GetTabletMapForShard(ctx, wr.ts, keyspace, shard)
	if err != nil {
		return err
	}

	// Check corner cases we're going to depend on
	masterElectTabletInfo, ok := tabletMap[*masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v is not in the shard", masterElectTabletAlias)
	}
	ev.NewMaster = *masterElectTabletInfo.Tablet
	if topo.TabletAliasEqual(shardInfo.MasterAlias, masterElectTabletAlias) {
		return fmt.Errorf("master-elect tablet %v is already the master", masterElectTabletAlias)
	}
	oldMasterTabletInfo, ok := tabletMap[*shardInfo.MasterAlias]
	if !ok {
		return fmt.Errorf("old master tablet %v is not in the shard", shardInfo.MasterAlias)
	}
	ev.OldMaster = *oldMasterTabletInfo.Tablet

	// Demote the current master, get its replication position
	wr.logger.Infof("demote current master %v", shardInfo.MasterAlias)
	event.DispatchUpdate(ev, "demoting old master")
	rp, err := wr.tmc.DemoteMaster(ctx, oldMasterTabletInfo)
	if err != nil {
		return fmt.Errorf("old master tablet %v DemoteMaster failed: %v", shardInfo.MasterAlias, err)
	}

	// Wait on the master-elect tablet until it reaches that position,
	// then promote it
	wr.logger.Infof("promote slave %v", masterElectTabletAlias)
	event.DispatchUpdate(ev, "promoting slave")
	rp, err = wr.tmc.PromoteSlaveWhenCaughtUp(ctx, masterElectTabletInfo, rp)
	if err != nil {
		return fmt.Errorf("master-elect tablet %v failed to catch up with replication or be upgraded to master: %v", masterElectTabletAlias, err)
	}

	// Go through all the tablets:
	// - new master: populate the reparent journal
	// - everybody else: reparent to new master, wait for row
	event.DispatchUpdate(ev, "reparenting all tablets")
	now := time.Now().UnixNano()
	wgMaster := sync.WaitGroup{}
	wgSlaves := sync.WaitGroup{}
	rec := concurrency.AllErrorRecorder{}
	var masterErr error
	for alias, tabletInfo := range tabletMap {
		if topo.TabletAliasEqual(&alias, masterElectTabletAlias) {
			wgMaster.Add(1)
			go func(alias pb.TabletAlias, tabletInfo *topo.TabletInfo) {
				defer wgMaster.Done()
				wr.logger.Infof("populating reparent journal on new master %v", alias)
				masterErr = wr.TabletManagerClient().PopulateReparentJournal(ctx, tabletInfo, now, plannedReparentShardOperation, &alias, rp)
			}(alias, tabletInfo)
		} else {
			wgSlaves.Add(1)
			go func(alias pb.TabletAlias, tabletInfo *topo.TabletInfo) {
				defer wgSlaves.Done()
				wr.logger.Infof("setting new master on slave %v", alias)
				// also restart replication on old master
				forceStartSlave := topo.TabletAliasEqual(&alias, oldMasterTabletInfo.Alias)
				if err := wr.TabletManagerClient().SetMaster(ctx, tabletInfo, masterElectTabletAlias, now, forceStartSlave); err != nil {
					rec.RecordError(fmt.Errorf("Tablet %v SetMaster failed: %v", alias, err))
					return
				}
			}(alias, tabletInfo)
		}
	}

	// After the master is done, we can update the shard record
	// (note with semi-sync, it also means at least one slave is done)
	wgMaster.Wait()
	if masterErr != nil {
		wgSlaves.Wait()
		return fmt.Errorf("failed to PopulateReparentJournal on master: %v", masterErr)
	}
	wr.logger.Infof("updating shard record with new master %v", masterElectTabletAlias)
	shardInfo.MasterAlias = masterElectTabletAlias
	if err := topo.UpdateShard(ctx, wr.ts, shardInfo); err != nil {
		wgSlaves.Wait()
		return fmt.Errorf("failed to update shard master record: %v", err)
	}

	// Wait for the slaves to complete. If some of them fail, we
	// will rebuild the shard serving graph anyway
	wgSlaves.Wait()
	if err := rec.Error(); err != nil {
		wr.Logger().Errorf("Some slaves failed to reparent: %v", err)
		return err
	}

	// Then we rebuild the entire serving graph for the shard,
//.........这里部分代码省略.........

func (wr *Wrangler) initShardMasterLocked(ctx context.Context, ev *events.Reparent, keyspace, shard string, masterElectTabletAlias *pb.TabletAlias, force bool, waitSlaveTimeout time.Duration) error {
	shardInfo, err := wr.ts.GetShard(ctx, keyspace, shard)
	if err != nil {
		return err
	}
	ev.ShardInfo = *shardInfo

	event.DispatchUpdate(ev, "reading tablet map")
	tabletMap, err := topo.GetTabletMapForShard(ctx, wr.ts, keyspace, shard)
	if err != nil {
		return err
	}

	// Check the master elect is in tabletMap
	masterElectTabletInfo, ok := tabletMap[*masterElectTabletAlias]
	if !ok {
		return fmt.Errorf("master-elect tablet %v is not in the shard", masterElectTabletAlias)
	}
	ev.NewMaster = *masterElectTabletInfo.Tablet

	// Check the master is the only master is the shard, or -force was used.
	_, masterTabletMap := topotools.SortedTabletMap(tabletMap)
	if !topo.TabletAliasEqual(shardInfo.MasterAlias, masterElectTabletAlias) {
		if !force {
			return fmt.Errorf("master-elect tablet %v is not the shard master, use -force to proceed anyway", masterElectTabletAlias)
		}
		wr.logger.Warningf("master-elect tablet %v is not the shard master, proceeding anyway as -force was used", masterElectTabletAlias)
	}
	if _, ok := masterTabletMap[*masterElectTabletAlias]; !ok {
		if !force {
			return fmt.Errorf("master-elect tablet %v is not a master in the shard, use -force to proceed anyway", masterElectTabletAlias)
		}
		wr.logger.Warningf("master-elect tablet %v is not a master in the shard, proceeding anyway as -force was used", masterElectTabletAlias)
	}
	haveOtherMaster := false
	for alias, ti := range masterTabletMap {
		if !topo.TabletAliasEqual(&alias, masterElectTabletAlias) && ti.Type != pb.TabletType_SCRAP {
			haveOtherMaster = true
		}
	}
	if haveOtherMaster {
		if !force {
			return fmt.Errorf("master-elect tablet %v is not the only master in the shard, use -force to proceed anyway", masterElectTabletAlias)
		}
		wr.logger.Warningf("master-elect tablet %v is not the only master in the shard, proceeding anyway as -force was used", masterElectTabletAlias)
	}

	// First phase: reset replication on all tablets. If anyone fails,
	// we stop. It is probably because it is unreachable, and may leave
	// an unstable database process in the mix, with a database daemon
	// at a wrong replication spot.
	event.DispatchUpdate(ev, "resetting replication on all tablets")
	wg := sync.WaitGroup{}
	rec := concurrency.AllErrorRecorder{}
	for alias, tabletInfo := range tabletMap {
		wg.Add(1)
		go func(alias pb.TabletAlias, tabletInfo *topo.TabletInfo) {
			defer wg.Done()
			wr.logger.Infof("resetting replication on tablet %v", alias)
			if err := wr.TabletManagerClient().ResetReplication(ctx, tabletInfo); err != nil {
				rec.RecordError(fmt.Errorf("Tablet %v ResetReplication failed (either fix it, or Scrap it): %v", alias, err))
			}
		}(alias, tabletInfo)
	}
	wg.Wait()
	if err := rec.Error(); err != nil {
		return err
	}

	// Tell the new master to break its slaves, return its replication
	// position
	wr.logger.Infof("initializing master on %v", masterElectTabletAlias)
	event.DispatchUpdate(ev, "initializing master")
	rp, err := wr.TabletManagerClient().InitMaster(ctx, masterElectTabletInfo)
	if err != nil {
		return err
	}

	// Now tell the new master to insert the reparent_journal row,
	// and tell everybody else to become a slave of the new master,