Golang topo.ShardInfo類代碼示例

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(context.TODO(), 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
}

// updateShardCellsAndMaster will update the 'Cells' and possibly
// MasterAlias records for the shard, if needed.
func (wr *Wrangler) updateShardCellsAndMaster(si *topo.ShardInfo, tabletAlias topo.TabletAlias, tabletType topo.TabletType, force bool) error {
	// See if we need to update the Shard:
	// - add the tablet's cell to the shard's Cells if needed
	// - change the master if needed
	shardUpdateRequired := false
	if !si.HasCell(tabletAlias.Cell) {
		shardUpdateRequired = true
	}
	if tabletType == topo.TYPE_MASTER && si.MasterAlias != tabletAlias {
		shardUpdateRequired = true
	}
	if !shardUpdateRequired {
		return nil
	}

	actionNode := actionnode.UpdateShard()
	keyspace := si.Keyspace()
	shard := si.ShardName()
	lockPath, err := wr.lockShard(keyspace, shard, actionNode)
	if err != nil {
		return err
	}

	// re-read the shard with the lock
	si, err = wr.ts.GetShard(keyspace, shard)
	if err != nil {
		return wr.unlockShard(keyspace, shard, actionNode, lockPath, err)
	}

	// update it
	wasUpdated := false
	if !si.HasCell(tabletAlias.Cell) {
		si.Cells = append(si.Cells, tabletAlias.Cell)
		wasUpdated = true
	}
	if tabletType == topo.TYPE_MASTER && si.MasterAlias != tabletAlias {
		if !si.MasterAlias.IsZero() && !force {
			return wr.unlockShard(keyspace, shard, actionNode, lockPath, fmt.Errorf("creating this tablet would override old master %v in shard %v/%v", si.MasterAlias, keyspace, shard))
		}
		si.MasterAlias = tabletAlias
		wasUpdated = true
	}

	if wasUpdated {
		// write it back
		if err := topo.UpdateShard(context.TODO(), wr.ts, si); err != nil {
			return wr.unlockShard(keyspace, shard, actionNode, lockPath, err)
		}
	}

	// and unlock
	return wr.unlockShard(keyspace, shard, actionNode, lockPath, err)
}

// replicaMigrateServedFrom handles the slave (replica, rdonly) migration.
func (wr *Wrangler) replicaMigrateServedFrom(ki *topo.KeyspaceInfo, sourceShard *topo.ShardInfo, destinationShard *topo.ShardInfo, servedType topo.TabletType, cells []string, reverse bool, tables []string, ev *events.MigrateServedFrom) error {
	// Save the destination keyspace (its ServedFrom has been changed)
	event.DispatchUpdate(ev, "updating keyspace")
	if err := topo.UpdateKeyspace(wr.ts, ki); err != nil {
		return err
	}

	// Save the source shard (its blacklisted tables field has changed)
	event.DispatchUpdate(ev, "updating source shard")
	if err := sourceShard.UpdateSourceBlacklistedTables(servedType, cells, reverse, tables); err != nil {
		return fmt.Errorf("UpdateSourceBlacklistedTables(%v/%v) failed: %v", sourceShard.Keyspace(), sourceShard.ShardName(), err)
	}
	if err := topo.UpdateShard(context.TODO(), wr.ts, sourceShard); err != nil {
		return fmt.Errorf("UpdateShard(%v/%v) failed: %v", sourceShard.Keyspace(), sourceShard.ShardName(), err)
	}

	// Now refresh the source servers so they reload their
	// blacklisted table list
	event.DispatchUpdate(ev, "refreshing sources tablets state so they update their blacklisted tables")
	if err := wr.RefreshTablesByShard(sourceShard, servedType, cells); err != nil {
		return err
	}

	return nil
}

func (wr *Wrangler) finishReparent(si *topo.ShardInfo, masterElect *topo.TabletInfo, majorityRestart, leaveMasterReadOnly bool) error {
	// If the majority of slaves restarted, move ahead.
	if majorityRestart {
		if leaveMasterReadOnly {
			wr.logger.Warningf("leaving master-elect read-only, change with: vtctl SetReadWrite %v", masterElect.Alias)
		} else {
			wr.logger.Infof("marking master-elect read-write %v", masterElect.Alias)
			if err := wr.tmc.SetReadWrite(wr.ctx, masterElect); err != nil {
				wr.logger.Warningf("master master-elect read-write failed, leaving master-elect read-only, change with: vtctl SetReadWrite %v", masterElect.Alias)
			}
		}
	} else {
		wr.logger.Warningf("minority reparent, manual fixes are needed, leaving master-elect read-only, change with: vtctl SetReadWrite %v", masterElect.Alias)
	}

	// save the new master in the shard info
	si.MasterAlias = masterElect.Alias
	if err := topo.UpdateShard(context.TODO(), wr.ts, si); err != nil {
		wr.logger.Errorf("Failed to save new master into shard: %v", err)
		return err
	}

	// We rebuild all the cells, as we may have taken tablets in and
	// out of the graph.
	wr.logger.Infof("rebuilding shard serving graph data")
	_, err := topotools.RebuildShard(context.TODO(), wr.logger, wr.ts, masterElect.Keyspace, masterElect.Shard, nil, wr.lockTimeout, interrupted)
	return err
}

func (zkts *Server) UpdateShard(si *topo.ShardInfo, existingVersion int64) (int64, error) {
	shardPath := path.Join(globalKeyspacesPath, si.Keyspace(), "shards", si.ShardName())
	stat, err := zkts.zconn.Set(shardPath, jscfg.ToJson(si.Shard), int(existingVersion))
	if err != nil {
		if zookeeper.IsError(err, zookeeper.ZNONODE) {
			err = topo.ErrNoNode
		}
		return -1, err
	}

	event.Dispatch(&events.ShardChange{
		ShardInfo: *si,
		Status:    "updated",
	})
	return int64(stat.Version()), nil
}

// RefreshTablesByShard calls RefreshState on all the tables of a
// given type in a shard. It would work for the master, but the
// discovery wouldn't be very efficient.
func (wr *Wrangler) RefreshTablesByShard(si *topo.ShardInfo, tabletType topo.TabletType, cells []string) error {
	wr.Logger().Infof("RefreshTablesByShard called on shard %v/%v", si.Keyspace(), si.ShardName())
	tabletMap, err := topo.GetTabletMapForShardByCell(context.TODO(), wr.ts, si.Keyspace(), si.ShardName(), cells)
	switch err {
	case nil:
		// keep going
	case topo.ErrPartialResult:
		wr.Logger().Warningf("RefreshTablesByShard: got partial result for shard %v/%v, may not refresh all tablets everywhere", si.Keyspace(), si.ShardName())
	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) {
			wr.Logger().Infof("Calling RefreshState on tablet %v", ti.Alias)
			if err := wr.tmc.RefreshState(wr.ctx, ti); err != nil {
				wr.Logger().Warningf("RefreshTablesByShard: failed to refresh %v: %v", ti.Alias, err)
			}
			wg.Done()
		}(ti)
	}
	wg.Wait()

	return nil
}

func (wr *Wrangler) migrateServedFrom(ki *topo.KeyspaceInfo, destinationShard *topo.ShardInfo, servedType topo.TabletType, cells []string, reverse bool) (err error) {

	// re-read and update keyspace info record
	ki, err = wr.ts.GetKeyspace(ki.KeyspaceName())
	if err != nil {
		return err
	}
	if reverse {
		ki.UpdateServedFromMap(servedType, cells, destinationShard.SourceShards[0].Keyspace, false, nil)
	} else {
		ki.UpdateServedFromMap(servedType, cells, destinationShard.SourceShards[0].Keyspace, true, destinationShard.Cells)
	}

	// re-read and check the destination shard
	destinationShard, err = wr.ts.GetShard(destinationShard.Keyspace(), destinationShard.ShardName())
	if err != nil {
		return err
	}
	if len(destinationShard.SourceShards) != 1 {
		return fmt.Errorf("Destination shard %v/%v is not a vertical split target", destinationShard.Keyspace(), destinationShard.ShardName())
	}
	tables := destinationShard.SourceShards[0].Tables

	// read the source shard, we'll need its master, and we'll need to
	// update the blacklisted tables.
	var sourceShard *topo.ShardInfo
	sourceShard, err = wr.ts.GetShard(destinationShard.SourceShards[0].Keyspace, destinationShard.SourceShards[0].Shard)
	if err != nil {
		return err
	}

	ev := &events.MigrateServedFrom{
		Keyspace:         *ki,
		SourceShard:      *sourceShard,
		DestinationShard: *destinationShard,
		ServedType:       servedType,
		Reverse:          reverse,
	}
	event.DispatchUpdate(ev, "start")
	defer func() {
		if err != nil {
			event.DispatchUpdate(ev, "failed: "+err.Error())
		}
	}()

	if servedType == topo.TYPE_MASTER {
		err = wr.masterMigrateServedFrom(ki, sourceShard, destinationShard, tables, ev)
	} else {
		err = wr.replicaMigrateServedFrom(ki, sourceShard, destinationShard, servedType, cells, reverse, tables, ev)
	}
	event.DispatchUpdate(ev, "finished")
	return
}

// rebuildCellSrvShard computes and writes the serving graph data to a
// single cell
func rebuildCellSrvShard(ctx context.Context, log logutil.Logger, ts topo.Server, shardInfo *topo.ShardInfo, cell string, tablets map[topo.TabletAlias]*topo.TabletInfo) error {
	log.Infof("rebuildCellSrvShard %v/%v in cell %v", shardInfo.Keyspace(), shardInfo.ShardName(), cell)

	// Get all existing db types so they can be removed if nothing
	// had been edited.
	existingTabletTypes, err := ts.GetSrvTabletTypesPerShard(cell, shardInfo.Keyspace(), shardInfo.ShardName())
	if err != nil {
		if err != topo.ErrNoNode {
			return err
		}
	}

	// Update db type addresses in the serving graph
	//
	// locationAddrsMap is a map:
	//   key: tabletType
	//   value: EndPoints (list of server records)
	locationAddrsMap := make(map[topo.TabletType]*topo.EndPoints)
	for _, tablet := range tablets {
		if !tablet.IsInReplicationGraph() {
			// only valid case is a scrapped master in the
			// catastrophic reparent case
			if tablet.Parent.Uid != topo.NO_TABLET {
				log.Warningf("Tablet %v should not be in the replication graph, please investigate (it is being ignored in the rebuild)", tablet.Alias)
			}
			continue
		}

		// Check IsInServingGraph, we don't want to add tablets that
		// are not serving
		if !tablet.IsInServingGraph() {
			continue
		}

		// Check the Keyspace and Shard for the tablet are right
		if tablet.Keyspace != shardInfo.Keyspace() || tablet.Shard != shardInfo.ShardName() {
			return fmt.Errorf("CRITICAL: tablet %v is in replication graph for shard %v/%v but belongs to shard %v:%v", tablet.Alias, shardInfo.Keyspace(), shardInfo.ShardName(), tablet.Keyspace, tablet.Shard)
		}

		// Add the tablet to the list
		addrs, ok := locationAddrsMap[tablet.Type]
		if !ok {
			addrs = topo.NewEndPoints()
			locationAddrsMap[tablet.Type] = addrs
		}
		entry, err := tablet.Tablet.EndPoint()
		if err != nil {
			log.Warningf("EndPointForTablet failed for tablet %v: %v", tablet.Alias, err)
			continue
		}
		addrs.Entries = append(addrs.Entries, *entry)
	}

	// we're gonna parallelize a lot here:
	// - writing all the tabletTypes records
	// - removing the unused records
	// - writing SrvShard
	rec := concurrency.AllErrorRecorder{}
	wg := sync.WaitGroup{}

	// write all the EndPoints nodes everywhere we want them
	for tabletType, addrs := range locationAddrsMap {
		wg.Add(1)
		go func(tabletType topo.TabletType, addrs *topo.EndPoints) {
			log.Infof("saving serving graph for cell %v shard %v/%v tabletType %v", cell, shardInfo.Keyspace(), shardInfo.ShardName(), tabletType)
			span := trace.NewSpanFromContext(ctx)
			span.StartClient("TopoServer.UpdateEndPoints")
			span.Annotate("tablet_type", string(tabletType))
			if err := ts.UpdateEndPoints(cell, shardInfo.Keyspace(), shardInfo.ShardName(), tabletType, addrs); err != nil {
				rec.RecordError(fmt.Errorf("writing endpoints for cell %v shard %v/%v tabletType %v failed: %v", cell, shardInfo.Keyspace(), shardInfo.ShardName(), tabletType, err))
			}
			span.Finish()
			wg.Done()
		}(tabletType, addrs)
	}

	// Delete any pre-existing paths that were not updated by this process.
	// That's the existingTabletTypes - locationAddrsMap
	for _, tabletType := range existingTabletTypes {
		if _, ok := locationAddrsMap[tabletType]; !ok {
			wg.Add(1)
			go func(tabletType topo.TabletType) {
				log.Infof("removing stale db type from serving graph: %v", tabletType)
				span := trace.NewSpanFromContext(ctx)
				span.StartClient("TopoServer.DeleteEndPoints")
				span.Annotate("tablet_type", string(tabletType))
				if err := ts.DeleteEndPoints(cell, shardInfo.Keyspace(), shardInfo.ShardName(), tabletType); err != nil {
					log.Warningf("unable to remove stale db type %v from serving graph: %v", tabletType, err)
				}
				span.Finish()
				wg.Done()
			}(tabletType)
		}
	}

	// Update srvShard object
	wg.Add(1)
	go func() {
//.........這裏部分代碼省略.........

func (wr *Wrangler) validateReplication(shardInfo *topo.ShardInfo, tabletMap map[topo.TabletAlias]*topo.TabletInfo, results chan<- error) {
	masterTablet, ok := tabletMap[shardInfo.MasterAlias]
	if !ok {
		results <- fmt.Errorf("master %v not in tablet map", shardInfo.MasterAlias)
		return
	}

	slaveList, err := wr.tmc.GetSlaves(wr.ctx, masterTablet)
	if err != nil {
		results <- fmt.Errorf("GetSlaves(%v) failed: %v", masterTablet, err)
		return
	}
	if len(slaveList) == 0 {
		results <- fmt.Errorf("no slaves of tablet %v found", shardInfo.MasterAlias)
		return
	}

	tabletIpMap := make(map[string]*topo.Tablet)
	slaveIpMap := make(map[string]bool)
	for _, tablet := range tabletMap {
		tabletIpMap[normalizeIP(tablet.IPAddr)] = tablet.Tablet
	}

	// See if every slave is in the replication graph.
	for _, slaveAddr := range slaveList {
		if tabletIpMap[normalizeIP(slaveAddr)] == nil {
			results <- fmt.Errorf("slave %v not in replication graph for shard %v/%v (mysql instance without vttablet?)", slaveAddr, shardInfo.Keyspace(), shardInfo.ShardName())
		}
		slaveIpMap[normalizeIP(slaveAddr)] = true
	}

	// See if every entry in the replication graph is connected to the master.
	for _, tablet := range tabletMap {
		if !tablet.IsSlaveType() {
			continue
		}

		if !slaveIpMap[normalizeIP(tablet.IPAddr)] {
			results <- fmt.Errorf("slave %v not replicating: %v %q", tablet.Alias, tablet.IPAddr, slaveList)
		}
	}
}

func (tee *Tee) UpdateShard(si *topo.ShardInfo, existingVersion int64) (newVersion int64, err error) {
	if newVersion, err = tee.primary.UpdateShard(si, existingVersion); err != nil {
		// failed on primary, not updating secondary
		return
	}

	// if we have a mapping between shard version in first topo
	// and shard version in second topo, replace the version number.
	// if not, this will probably fail and log.
	tee.mu.Lock()
	svm, ok := tee.shardVersionMapping[si.Keyspace()+"/"+si.ShardName()]
	if ok && svm.readFromVersion == existingVersion {
		existingVersion = svm.readFromSecondVersion
		delete(tee.shardVersionMapping, si.Keyspace()+"/"+si.ShardName())
	}
	tee.mu.Unlock()
	if newVersion2, serr := tee.secondary.UpdateShard(si, existingVersion); serr != nil {
		// not critical enough to fail
		if serr == topo.ErrNoNode {
			// the shard doesn't exist on the secondary, let's
			// just create it
			if serr = tee.secondary.CreateShard(si.Keyspace(), si.ShardName(), si.Shard); serr != nil {
				log.Warningf("secondary.CreateShard(%v,%v) failed (after UpdateShard returned ErrNoNode): %v", si.Keyspace(), si.ShardName(), serr)
			} else {
				log.Infof("secondary.UpdateShard(%v, %v) failed with ErrNoNode, CreateShard then worked.", si.Keyspace(), si.ShardName())
				si, gerr := tee.secondary.GetShard(si.Keyspace(), si.ShardName())
				if gerr != nil {
					log.Warningf("Failed to re-read shard(%v, %v) after creating it on secondary: %v", si.Keyspace(), si.ShardName(), gerr)
				} else {
					tee.mu.Lock()
					tee.shardVersionMapping[si.Keyspace()+"/"+si.ShardName()] = versionMapping{
						readFromVersion:       newVersion,
						readFromSecondVersion: si.Version(),
					}
					tee.mu.Unlock()
				}
			}
		} else {
			log.Warningf("secondary.UpdateShard(%v, %v) failed: %v", si.Keyspace(), si.ShardName(), serr)
		}
	} else {
		tee.mu.Lock()
		tee.shardVersionMapping[si.Keyspace()+"/"+si.ShardName()] = versionMapping{
			readFromVersion:       newVersion,
			readFromSecondVersion: newVersion2,
		}
		tee.mu.Unlock()
	}
	return
}

// masterMigrateServedFrom handles the master migration. The ordering is
// a bit different than for rdonly / replica to guarantee a smooth transition.
//
// The order is as follows:
// - Add BlacklistedTables on the source shard map for master
// - Refresh the source master, so it stops writing on the tables
// - Get the source master position, wait until destination master reaches it
// - Clear SourceShard on the destination Shard
// - Refresh the destination master, so its stops its filtered
//   replication and starts accepting writes
func (wr *Wrangler) masterMigrateServedFrom(ki *topo.KeyspaceInfo, sourceShard *topo.ShardInfo, destinationShard *topo.ShardInfo, tables []string, ev *events.MigrateServedFrom) error {
	// Read the data we need
	sourceMasterTabletInfo, err := wr.ts.GetTablet(sourceShard.MasterAlias)
	if err != nil {
		return err
	}
	destinationMasterTabletInfo, err := wr.ts.GetTablet(destinationShard.MasterAlias)
	if err != nil {
		return err
	}

	// Update source shard (more blacklisted tables)
	event.DispatchUpdate(ev, "updating source shard")
	if err := sourceShard.UpdateSourceBlacklistedTables(topo.TYPE_MASTER, nil, false, tables); err != nil {
		return fmt.Errorf("UpdateSourceBlacklistedTables(%v/%v) failed: %v", sourceShard.Keyspace(), sourceShard.ShardName(), err)
	}
	if err := topo.UpdateShard(context.TODO(), wr.ts, sourceShard); err != nil {
		return fmt.Errorf("UpdateShard(%v/%v) failed: %v", sourceShard.Keyspace(), sourceShard.ShardName(), err)
	}

	// Now refresh the blacklisted table list on the source master
	event.DispatchUpdate(ev, "refreshing source master so it updates its blacklisted tables")
	if err := wr.tmc.RefreshState(wr.ctx, sourceMasterTabletInfo); err != nil {
		return err
	}

	// get the position
	event.DispatchUpdate(ev, "getting master position")
	masterPosition, err := wr.tmc.MasterPosition(wr.ctx, sourceMasterTabletInfo)
	if err != nil {
		return err
	}

	// wait for it
	event.DispatchUpdate(ev, "waiting for destination master to catch up to source master")
	if err := wr.tmc.WaitBlpPosition(context.TODO(), destinationMasterTabletInfo, blproto.BlpPosition{
		Uid:      0,
		Position: masterPosition,
	}, wr.ActionTimeout()); err != nil {
		return err
	}

	// Update the destination keyspace (its ServedFrom has changed)
	event.DispatchUpdate(ev, "updating keyspace")
	if err = topo.UpdateKeyspace(wr.ts, ki); err != nil {
		return err
	}

	// Update the destination shard (no more source shard)
	event.DispatchUpdate(ev, "updating destination shard")
	destinationShard.SourceShards = nil
	if err := topo.UpdateShard(context.TODO(), wr.ts, destinationShard); err != nil {
		return err
	}

	// Tell the new shards masters they can now be read-write.
	// Invoking a remote action will also make the tablet stop filtered
	// replication.
	event.DispatchUpdate(ev, "setting destination shard masters read-write")
	if err := wr.refreshMasters([]*topo.ShardInfo{destinationShard}); err != nil {
		return err
	}

	return nil
}

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(context.TODO(), wr.ts, shardInfo.Keyspace(), shardInfo.ShardName())
		if err != nil {
			return nil, err
		}

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

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

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

		err = wr.reparentShardGraceful(ev, 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 (wr *Wrangler) applySchemaShard(shardInfo *topo.ShardInfo, preflight *myproto.SchemaChangeResult, masterTabletAlias topo.TabletAlias, change string, newParentTabletAlias topo.TabletAlias, simple, force bool) (*myproto.SchemaChangeResult, error) {

	// find all the shards we need to handle
	aliases, err := topo.FindAllTabletAliasesInShard(context.TODO(), wr.ts, shardInfo.Keyspace(), shardInfo.ShardName())
	if err != nil {
		return nil, err
	}

	// build the array of TabletStatus we're going to use
	statusArray := make([]*TabletStatus, 0, len(aliases)-1)
	for _, alias := range aliases {
		if alias == masterTabletAlias {
			// we skip the master
			continue
		}

		ti, err := wr.ts.GetTablet(alias)
		if err != nil {
			return nil, err
		}
		if ti.Type == topo.TYPE_LAG {
			// lag tablets are usually behind, not replicating,
			// and a general pain. So let's just skip them
			// all together.
			// TODO(alainjobart) figure out other types to skip:
			// ValidateSchemaShard only does the serving types.
			// We do everything in the replication graph
			// but LAG. This seems fine for now.
			log.Infof("Skipping tablet %v as it is LAG", ti.Alias)
			continue
		}

		statusArray = append(statusArray, &TabletStatus{ti: ti})
	}

	// get schema on all tablets.
	log.Infof("Getting schema on all tablets for shard %v/%v", shardInfo.Keyspace(), shardInfo.ShardName())
	wg := &sync.WaitGroup{}
	for _, status := range statusArray {
		wg.Add(1)
		go func(status *TabletStatus) {
			status.beforeSchema, status.lastError = wr.tmc.GetSchema(wr.ctx, status.ti, nil, nil, false)
			wg.Done()
		}(status)
	}
	wg.Wait()

	// quick check for errors
	for _, status := range statusArray {
		if status.lastError != nil {
			return nil, fmt.Errorf("Error getting schema on tablet %v: %v", status.ti.Alias, status.lastError)
		}
	}

	// simple or complex?
	if simple {
		return wr.applySchemaShardSimple(statusArray, preflight, masterTabletAlias, change, force)
	}

	return wr.applySchemaShardComplex(statusArray, shardInfo, preflight, masterTabletAlias, change, newParentTabletAlias, force)
}

// reparentShardBrutal executes a brutal reparent.
//
// Assume the master is dead and not coming back. Just push your way
// forward.  Force means we are reparenting to the same master
// (assuming the data has been externally synched).
//
// The ev parameter is an event struct prefilled with information that the
// caller has on hand, which would be expensive for us to re-query.
func (wr *Wrangler) reparentShardBrutal(ev *events.Reparent, si *topo.ShardInfo, slaveTabletMap, masterTabletMap map[topo.TabletAlias]*topo.TabletInfo, masterElectTablet *topo.TabletInfo, leaveMasterReadOnly, force bool) (err error) {
	event.DispatchUpdate(ev, "starting brutal")

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

	wr.logger.Infof("Skipping ValidateShard - not a graceful situation")

	if _, ok := slaveTabletMap[masterElectTablet.Alias]; !ok && !force {
		return fmt.Errorf("master elect tablet not in replication graph %v %v/%v %v", masterElectTablet.Alias, si.Keyspace(), si.ShardName(), topotools.MapKeys(slaveTabletMap))
	}

	// Check the master-elect and slaves are in good shape when the action
	// has not been forced.
	if !force {
		// Make sure all tablets have the right parent and reasonable positions.
		event.DispatchUpdate(ev, "checking slave replication positions")
		if err := wr.checkSlaveReplication(slaveTabletMap, topo.NO_TABLET); err != nil {
			return err
		}

		// Check the master-elect is fit for duty - call out for hardware checks.
		event.DispatchUpdate(ev, "checking that new master is ready to serve")
		if err := wr.checkMasterElect(masterElectTablet); err != nil {
			return err
		}

		event.DispatchUpdate(ev, "checking slave consistency")
		wr.logger.Infof("check slaves %v/%v", masterElectTablet.Keyspace, masterElectTablet.Shard)
		restartableSlaveTabletMap := wr.restartableTabletMap(slaveTabletMap)
		err = wr.checkSlaveConsistency(restartableSlaveTabletMap, myproto.ReplicationPosition{})
		if err != nil {
			return err
		}
	} else {
		event.DispatchUpdate(ev, "stopping slave replication")
		wr.logger.Infof("forcing reparent to same master %v", masterElectTablet.Alias)
		err := wr.breakReplication(slaveTabletMap, masterElectTablet)
		if err != nil {
			return err
		}
	}

	event.DispatchUpdate(ev, "promoting new master")
	rsd, err := wr.promoteSlave(masterElectTablet)
	if err != nil {
		// FIXME(msolomon) This suggests that the master-elect is dead.
		// We need to classify certain errors as temporary and retry.
		return fmt.Errorf("promote slave failed: %v %v", err, masterElectTablet.Alias)
	}

	// Once the slave is promoted, remove it from our maps
	delete(slaveTabletMap, masterElectTablet.Alias)
	delete(masterTabletMap, masterElectTablet.Alias)

	event.DispatchUpdate(ev, "restarting slaves")
	majorityRestart, restartSlaveErr := wr.restartSlaves(slaveTabletMap, rsd)

	if !force {
		for _, failedMaster := range masterTabletMap {
			event.DispatchUpdate(ev, "scrapping old master")
			wr.logger.Infof("scrap dead master %v", failedMaster.Alias)
			// The master is dead so execute the action locally instead of
			// enqueing the scrap action for an arbitrary amount of time.
			if scrapErr := topotools.Scrap(wr.ts, failedMaster.Alias, false); scrapErr != nil {
				wr.logger.Warningf("scrapping failed master failed: %v", scrapErr)
			}
		}
	}

	event.DispatchUpdate(ev, "rebuilding shard serving graph")
	err = wr.finishReparent(si, masterElectTablet, majorityRestart, leaveMasterReadOnly)
	if err != nil {
		return err
	}

	event.DispatchUpdate(ev, "finished")

	if restartSlaveErr != nil {
		// This is more of a warning at this point.
		return restartSlaveErr
	}

	return nil
}