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(context.TODO(), 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
}
// Check all the tablets to see if we can proceed with reparenting.
// masterPosition is supplied from the demoted master if we are doing
// this gracefully.
func (wr *Wrangler) checkSlaveConsistency(tabletMap map[uint32]*topo.TabletInfo, masterPosition myproto.ReplicationPosition) error {
wr.logger.Infof("checkSlaveConsistency %v %#v", topotools.MapKeys(tabletMap), masterPosition)
// FIXME(msolomon) Something still feels clumsy here and I can't put my finger on it.
calls := make(chan *rpcContext, len(tabletMap))
f := func(ti *topo.TabletInfo) {
ctx := &rpcContext{tablet: ti}
defer func() {
calls <- ctx
}()
if !masterPosition.IsZero() {
// If the master position is known, do our best to wait for replication to catch up.
status, err := wr.tmc.WaitSlavePosition(context.TODO(), ti, masterPosition, wr.ActionTimeout())
if err != nil {
ctx.err = err
return
}
ctx.status = status
} else {
// If the master is down, just get the slave status.
status, err := wr.tmc.SlaveStatus(wr.ctx, ti)
if err != nil {
ctx.err = err
return
}
ctx.status = status
}
}
for _, tablet := range tabletMap {
// Pass loop variable explicitly so we don't have a concurrency issue.
go f(tablet)
}
// map positions to tablets
positionMap := make(map[string][]uint32)
for i := 0; i < len(tabletMap); i++ {
ctx := <-calls
mapKey := "unavailable-tablet-error"
if ctx.err == nil {
mapKey = ctx.status.Position.String()
}
if _, ok := positionMap[mapKey]; !ok {
positionMap[mapKey] = make([]uint32, 0, 32)
}
positionMap[mapKey] = append(positionMap[mapKey], ctx.tablet.Alias.Uid)
}
if len(positionMap) == 1 {
// great, everyone agrees
// demotedMasterReplicationState is nil if demotion failed
if !masterPosition.IsZero() {
demotedMapKey := masterPosition.String()
if _, ok := positionMap[demotedMapKey]; !ok {
for slaveMapKey := range positionMap {
return fmt.Errorf("slave position doesn't match demoted master: %v != %v", demotedMapKey,
slaveMapKey)
}
}
}
} else {
// FIXME(msolomon) in the event of a crash, do you pick replica that is
// furthest along or do you promote the majority? data loss vs availability
// sounds like you pick the latest group and reclone.
items := make([]string, 0, 32)
for slaveMapKey, uids := range positionMap {
tabletPaths := make([]string, len(uids))
for i, uid := range uids {
tabletPaths[i] = tabletMap[uid].Alias.String()
}
items = append(items, fmt.Sprintf(" %v\n %v", slaveMapKey, strings.Join(tabletPaths, "\n ")))
}
sort.Strings(items)
return fmt.Errorf("inconsistent slaves, mark some offline with vtctl ScrapTablet\n%v", strings.Join(items, "\n"))
}
return nil
}
// tabletExternallyReparentedLocked is called with the shard lock.
// It returns if agent.refreshTablet should be called, and the error.
// Note both are set independently (can have both true and an error).
func (agent *ActionAgent) tabletExternallyReparentedLocked(ctx context.Context, externalID string, interrupted chan struct{}) (bool, error) {
// re-read the tablet record to be sure we have the latest version
tablet, err := agent.TopoServer.GetTablet(agent.TabletAlias)
if err != nil {
return false, err
}
// read the shard, make sure again the master is not already good.
shardInfo, err := agent.TopoServer.GetShard(tablet.Keyspace, tablet.Shard)
if err != nil {
return false, err
}
if shardInfo.MasterAlias == tablet.Alias {
log.Infof("TabletExternallyReparented: tablet became the master before we get the lock?")
return false, nil
}
log.Infof("TabletExternallyReparented called and we're not the master, doing the work")
// 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(ctx, agent.TopoServer, 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 false, err
}
masterElectTablet, ok := tabletMap[tablet.Alias]
if !ok {
return false, 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,
ExternalID: externalID,
}
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.
// Note after this call, we may have changed the tablet record,
// so we will always return true, so the tablet record is re-read
// by the agent.
event.DispatchUpdate(ev, "mark ourself as new master")
err = agent.updateReplicationGraphForPromotedSlave(ctx, tablet)
if err != nil {
// This suggests we can't talk to topo server. This is bad.
return true, 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()
tmc := tmclient.NewTabletManagerClient()
topotools.RestartSlavesExternal(agent.TopoServer, logger, slaveTabletMap, masterTabletMap, masterElectTablet.Alias, func(ti *topo.TabletInfo, swrd *actionnode.SlaveWasRestartedArgs) error {
return tmc.SlaveWasRestarted(ctx, ti, swrd)
})
// 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(ctx, agent.TopoServer, shardInfo); err != nil {
return true, 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(ctx, logger, agent.TopoServer, tablet.Keyspace, tablet.Shard, cells, agent.LockTimeout, interrupted); err != nil {
return true, err
}
event.DispatchUpdate(ev, "finished")
return true, nil
}
// reparentShardGraceful executes a graceful reparent.
// 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) reparentShardGraceful(ev *events.Reparent, si *topo.ShardInfo, slaveTabletMap, masterTabletMap map[topo.TabletAlias]*topo.TabletInfo, masterElectTablet *topo.TabletInfo, leaveMasterReadOnly bool) (err error) {
event.DispatchUpdate(ev, "starting graceful")
defer func() {
if err != nil {
event.DispatchUpdate(ev, "failed: "+err.Error())
}
}()
// Validate a bunch of assumptions we make about the replication graph.
if len(masterTabletMap) != 1 {
aliases := make([]string, 0, len(masterTabletMap))
for _, v := range masterTabletMap {
aliases = append(aliases, v.String())
}
return fmt.Errorf("I have 0 or multiple masters / scrapped tablets in this shard replication graph, please scrap the non-master ones: %v", strings.Join(aliases, " "))
}
var masterTablet *topo.TabletInfo
for _, v := range masterTabletMap {
masterTablet = v
}
if masterTablet.Parent.Uid != topo.NO_TABLET {
return fmt.Errorf("master tablet should not have a ParentUid: %v %v", masterTablet.Parent.Uid, masterTablet.Alias)
}
if masterTablet.Type != topo.TYPE_MASTER {
return fmt.Errorf("master tablet should not be type: %v %v", masterTablet.Type, masterTablet.Alias)
}
if masterTablet.Alias.Uid == masterElectTablet.Alias.Uid {
return fmt.Errorf("master tablet should not match master elect - this must be forced: %v", masterTablet.Alias)
}
if _, ok := slaveTabletMap[masterElectTablet.Alias]; !ok {
return fmt.Errorf("master elect tablet not in replication graph %v %v/%v %v", masterElectTablet.Alias, masterTablet.Keyspace, masterTablet.Shard, topotools.MapKeys(slaveTabletMap))
}
if err := wr.ValidateShard(masterTablet.Keyspace, masterTablet.Shard, true); err != nil {
return fmt.Errorf("ValidateShard verification failed: %v, if the master is dead, run: vtctl ScrapTablet -force %v", err, masterTablet.Alias)
}
// Make sure all tablets have the right parent and reasonable positions.
event.DispatchUpdate(ev, "checking slave replication positions")
err = wr.checkSlaveReplication(slaveTabletMap, masterTablet.Alias.Uid)
if 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")
err = wr.checkMasterElect(masterElectTablet)
if err != nil {
return err
}
event.DispatchUpdate(ev, "demoting old master")
masterPosition, err := wr.demoteMaster(masterTablet)
if err != nil {
// FIXME(msolomon) This suggests that the master is dead and we
// need to take steps. We could either pop a prompt, or make
// retrying the action painless.
return fmt.Errorf("demote master failed: %v, if the master is dead, run: vtctl -force ScrapTablet %v", err, masterTablet.Alias)
}
event.DispatchUpdate(ev, "checking slave consistency")
wr.logger.Infof("check slaves %v/%v", masterTablet.Keyspace, masterTablet.Shard)
restartableSlaveTabletMap := wr.restartableTabletMap(slaveTabletMap)
err = wr.checkSlaveConsistency(restartableSlaveTabletMap, masterPosition)
if err != nil {
return fmt.Errorf("check slave consistency failed %v, demoted master is still read only, run: vtctl SetReadWrite %v", err, masterTablet.Alias)
}
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, demoted master is still read only: vtctl SetReadWrite %v", err, masterTablet.Alias)
}
// Once the slave is promoted, remove it from our map
delete(slaveTabletMap, masterElectTablet.Alias)
event.DispatchUpdate(ev, "restarting slaves")
majorityRestart, restartSlaveErr := wr.restartSlaves(slaveTabletMap, rsd)
// For now, scrap the old master regardless of how many
// slaves restarted.
//
// FIXME(msolomon) We could reintroduce it and reparent it and use
// it as new replica.
event.DispatchUpdate(ev, "scrapping old master")
wr.logger.Infof("scrap demoted master %v", masterTablet.Alias)
if scrapErr := wr.tmc.Scrap(wr.ctx, masterTablet); scrapErr != nil {
// The sub action is non-critical, so just warn.
wr.logger.Warningf("scrap demoted 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
}
// 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
}