supporting --panic-flag-file; when it exists - app panics and exits without cleanup

build.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 #
 #
-RELEASE_VERSION="0.9.3"
+RELEASE_VERSION="0.9.4"
 
 buildpath=/tmp/gh-ost
 target=gh-ost

go/base/context.go

@@ -70,6 +70,7 @@ type MigrationContext struct {
 	maxLoadMutex                        *sync.Mutex
 	PostponeCutOverFlagFile             string
 	SwapTablesTimeoutSeconds            int64
+	PanicFlagFile                       string
 
 	ServeSocketFile string
 	ServeTCPPort    int64

go/cmd/gh-ost/main.go

@@ -76,6 +76,7 @@ func main() {
 	flag.StringVar(&migrationContext.ThrottleFlagFile, "throttle-flag-file", "", "operation pauses when this file exists; hint: use a file that is specific to the table being altered")
 	flag.StringVar(&migrationContext.ThrottleAdditionalFlagFile, "throttle-additional-flag-file", "/tmp/gh-ost.throttle", "operation pauses when this file exists; hint: keep default, use for throttling multiple gh-ost operations")
 	flag.StringVar(&migrationContext.PostponeCutOverFlagFile, "postpone-cut-over-flag-file", "", "while this file exists, migration will postpone the final stage of swapping tables, and will keep on syncing the ghost table. Cut-over/swapping would be ready to perform the moment the file is deleted.")
+	flag.StringVar(&migrationContext.PanicFlagFile, "panic-flag-file", "", "when this file is created, gh-ost will immediately terminate, without cleanup")
 
 	flag.StringVar(&migrationContext.ServeSocketFile, "serve-socket-file", "", "Unix socket file to serve on. Default: auto-determined and advertised upon startup")
 	flag.Int64Var(&migrationContext.ServeTCPPort, "serve-tcp-port", 0, "TCP port to serve on. Default: disabled")

go/logic/migrator.go

@@ -99,6 +99,15 @@ func (this *Migrator) acceptSignals() {
 }
 
 func (this *Migrator) shouldThrottle() (result bool, reason string) {
+
+	// Regardless of throttle, we take opportunity to check for panic-abort
+	if this.migrationContext.PanicFlagFile != "" {
+		if base.FileExists(this.migrationContext.PanicFlagFile) {
+			this.panicAbort <- fmt.Errorf("Found panic-file %s. Aborting without cleanup", this.migrationContext.PanicFlagFile)
+		}
+	}
+	// Back to throttle considerations
+
 	// User-based throttle
 	if atomic.LoadInt64(&this.migrationContext.ThrottleCommandedByUser) > 0 {
 		return true, "commanded by user"
@@ -295,6 +304,7 @@ func (this *Migrator) listenOnPanicAbort() {
 	err := <-this.panicAbort
 	log.Fatale(err)
 }
+
 func (this *Migrator) validateStatement() (err error) {
 	if this.parser.HasNonTrivialRenames() && !this.migrationContext.SkipRenamedColumns {
 		this.migrationContext.ColumnRenameMap = this.parser.GetNonTrivialRenames()
@@ -606,12 +616,14 @@ func (this *Migrator) onServerCommand(command string, writer *bufio.Writer) (err
 	if len(tokens) > 1 {
 		arg = strings.TrimSpace(tokens[1])
 	}
+
 	switch command {
 	case "help":
 		{
 			fmt.Fprintln(writer, `available commands:
   status               # Print a status message
   chunk-size=<newsize> # Set a new chunk-size
+	max-load=<maxload>   # Set a new set of max-load thresholds
   throttle             # Force throttling
   no-throttle          # End forced throttling (other throttling may still apply)
   help                 # This message
@@ -740,6 +752,16 @@ func (this *Migrator) printMigrationStatusHint(writers ...io.Writer) {
 			this.migrationContext.ThrottleAdditionalFlagFile,
 		))
 	}
+	if this.migrationContext.PostponeCutOverFlagFile != "" {
+		fmt.Fprintln(w, fmt.Sprintf("# Postpone cut-over flag file: %+v",
+			this.migrationContext.PostponeCutOverFlagFile,
+		))
+	}
+	if this.migrationContext.PanicFlagFile != "" {
+		fmt.Fprintln(w, fmt.Sprintf("# Panic flag file: %+v",
+			this.migrationContext.PanicFlagFile,
+		))
+	}
 	fmt.Fprintln(w, fmt.Sprintf("# Serving on unix socket: %+v",
 		this.migrationContext.ServeSocketFile,
 	))