supporting --force-named-cut-over

- when given, user _must_ specify table name
  and of course table name must match migrated table

Author: Shlomi Noach

go/base/context.go

@@ -92,6 +92,7 @@ type MigrationContext struct {
 	criticalLoad                        LoadMap
 	PostponeCutOverFlagFile             string
 	CutOverLockTimeoutSeconds           int64
+	ForceNamedCutOverCommand            bool
 	PanicFlagFile                       string
 	HooksPath                           string
 	HooksHintMessage                    string

go/cmd/gh-ost/main.go

@@ -71,6 +71,7 @@ func main() {
 	flag.BoolVar(&migrationContext.InitiallyDropOldTable, "initially-drop-old-table", false, "Drop a possibly existing OLD table (remains from a previous run?) before beginning operation. Default is to panic and abort if such table exists")
 	flag.BoolVar(&migrationContext.InitiallyDropGhostTable, "initially-drop-ghost-table", false, "Drop a possibly existing Ghost table (remains from a previous run?) before beginning operation. Default is to panic and abort if such table exists")
 	cutOver := flag.String("cut-over", "atomic", "choose cut-over type (default|atomic, two-step)")
+	flag.BoolVar(&migrationContext.ForceNamedCutOverCommand, "force-named-cut-over", false, "When true, the 'unpostpone|cut-over' interactive command must name the migrated table")
 
 	flag.BoolVar(&migrationContext.SwitchToRowBinlogFormat, "switch-to-rbr", false, "let this tool automatically switch binary log format to 'ROW' on the replica, if needed. The format will NOT be switched back. I'm too scared to do that, and wish to protect you if you happen to execute another migration while this one is running")
 	flag.BoolVar(&migrationContext.AssumeRBR, "assume-rbr", false, "set to 'true' when you know for certain your server uses 'ROW' binlog_format. gh-ost is unable to tell, event after reading binlog_format, whether the replication process does indeed use 'ROW', and restarts replication to be certain RBR setting is applied. Such operation requires SUPER privileges which you might not have. Setting this flag avoids restarting replication and you can proceed to use gh-ost without SUPER privileges")

go/logic/server.go

@@ -231,12 +231,14 @@ help                                 # This message
 		}
 	case "unpostpone", "no-postpone", "cut-over":
 		{
-			if arg != "" {
-				if arg != this.migrationContext.OriginalTableName {
-					// User exlpicitly provided table name. This is a courtesy protection mechanism
-					err := fmt.Errorf("User commanded 'unpostpone' on %s, but migrated table is %s; ingoring request.", arg, this.migrationContext.OriginalTableName)
-					return NoPrintStatusRule, err
-				}
+			if arg == "" && this.migrationContext.ForceNamedCutOverCommand {
+				err := fmt.Errorf("User commanded 'unpostpone' without specifying table name, but --force-named-cut-over is set")
+				return NoPrintStatusRule, err
+			}
+			if arg != "" && arg != this.migrationContext.OriginalTableName {
+				// User exlpicitly provided table name. This is a courtesy protection mechanism
+				err := fmt.Errorf("User commanded 'unpostpone' on %s, but migrated table is %s; ingoring request.", arg, this.migrationContext.OriginalTableName)
+				return NoPrintStatusRule, err
 			}
 			if atomic.LoadInt64(&this.migrationContext.IsPostponingCutOver) > 0 {
 				atomic.StoreInt64(&this.migrationContext.UserCommandedUnpostponeFlag, 1)