// Return a replication state that will reparent a slave to the
// correct master for a specified position.
func (mysqld *Mysqld) ReparentPosition(slavePosition *proto.ReplicationPosition) (rs *proto.ReplicationState, waitPosition *proto.ReplicationPosition, reparentTime int64, err error) {
qr, err := mysqld.fetchSuperQuery(fmt.Sprintf("SELECT time_created_ns, new_addr, new_position, wait_position FROM _vt.reparent_log WHERE last_position = '%v'", slavePosition.MapKey()))
if err != nil {
return
}
if len(qr.Rows) != 1 {
err = fmt.Errorf("no reparent for position: %v", slavePosition.MapKey())
return
}
reparentTime, err = qr.Rows[0][0].ParseInt64()
if err != nil {
err = fmt.Errorf("bad reparent time: %v %v %v", slavePosition.MapKey(), qr.Rows[0][0], err)
return
}
file, pos, err := parseReplicationPosition(qr.Rows[0][2].String())
if err != nil {
return
}
rs, err = proto.NewReplicationState(qr.Rows[0][1].String())
if err != nil {
return
}
rs.ReplicationPosition.MasterLogFile = file
rs.ReplicationPosition.MasterLogPosition = uint(pos)
file, pos, err = parseReplicationPosition(qr.Rows[0][3].String())
if err != nil {
return
}
waitPosition = new(proto.ReplicationPosition)
waitPosition.MasterLogFile = file
waitPosition.MasterLogPosition = pos
return
}
// 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 {
log.V(6).Infof("checkSlaveConsistency %v %#v", 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
}()
var args *myproto.ReplicationPosition
if masterPosition != nil {
// If the master position is known, do our best to wait for replication to catch up.
args = masterPosition
} else {
// In the case where a master is down, look for the last bit of data copied and wait
// for that to apply. That gives us a chance to wait for all data.
replPos, err := wr.ai.SlavePosition(ti, wr.actionTimeout())
if err != nil {
ctx.err = err
return
}
args = &myproto.ReplicationPosition{
MasterLogFile: replPos.MasterLogFileIo,
MasterLogPositionIo: replPos.MasterLogPositionIo,
}
}
// This option waits for the SQL thread to apply all changes to this instance.
rp, err := wr.ai.WaitSlavePosition(ti, args, wr.actionTimeout())
if err != nil {
ctx.err = err
return
}
ctx.position = rp
}
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.position.MapKey()
}
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 != nil {
demotedMapKey := masterPosition.MapKey()
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
}