initial support for --resurrect flag

go/base/context.go

@@ -82,6 +82,7 @@ type MigrationContext struct {
 	SkipRenamedColumns       bool
 	IsTungsten               bool
 	DiscardForeignKeys       bool
+	Resurrect                bool
 
 	config            ContextConfig
 	configMutex       *sync.Mutex
@@ -161,6 +162,7 @@ type MigrationContext struct {
 	UserCommandedUnpostponeFlag            int64
 	CutOverCompleteFlag                    int64
 	InCutOverCriticalSectionFlag           int64
+	IsResurrected                          bool
 
 	OriginalTableColumnsOnApplier    *sql.ColumnList
 	OriginalTableColumns             *sql.ColumnList

go/cmd/gh-ost/main.go

@@ -58,6 +58,7 @@ func main() {
 	flag.StringVar(&migrationContext.DatabaseName, "database", "", "database name (mandatory)")
 	flag.StringVar(&migrationContext.OriginalTableName, "table", "", "table name (mandatory)")
 	flag.StringVar(&migrationContext.AlterStatement, "alter", "", "alter statement (mandatory)")
+
 	flag.BoolVar(&migrationContext.CountTableRows, "exact-rowcount", false, "actually count table rows as opposed to estimate them (results in more accurate progress estimation)")
 	flag.BoolVar(&migrationContext.ConcurrentCountTableRows, "concurrent-rowcount", true, "(with --exact-rowcount), when true (default): count rows after row-copy begins, concurrently, and adjust row estimate later on; when false: first count rows, then start row copy")
 	flag.BoolVar(&migrationContext.AllowedRunningOnMaster, "allow-on-master", false, "allow this migration to run directly on master. Preferably it would run on a replica")
@@ -68,6 +69,7 @@ func main() {
 	flag.BoolVar(&migrationContext.IsTungsten, "tungsten", false, "explicitly let gh-ost know that you are running on a tungsten-replication based topology (you are likely to also provide --assume-master-host)")
 	flag.BoolVar(&migrationContext.DiscardForeignKeys, "discard-foreign-keys", false, "DANGER! This flag will migrate a table that has foreign keys and will NOT create foreign keys on the ghost table, thus your altered table will have NO foreign keys. This is useful for intentional dropping of foreign keys")
 	flag.BoolVar(&migrationContext.SkipForeignKeyChecks, "skip-foreign-key-checks", false, "set to 'true' when you know for certain there are no foreign keys on your table, and wish to skip the time it takes for gh-ost to verify that")
+	flag.BoolVar(&migrationContext.Resurrect, "resurrect", false, "resume previously crashed migration")
 
 	executeFlag := flag.Bool("execute", false, "actually execute the alter & migrate the table. Default is noop: do some tests and exit")
 	flag.BoolVar(&migrationContext.TestOnReplica, "test-on-replica", false, "Have the migration run on a replica, not on the master. At the end of migration replication is stopped, and tables are swapped and immediately swap-revert. Replication remains stopped and you can compare the two tables for building trust")
@@ -178,6 +180,12 @@ func main() {
 	if *cliMasterPassword != "" && migrationContext.AssumeMasterHostname == "" {
 		log.Fatalf("--master-password requires --assume-master-host")
 	}
+	if migrationContext.InitiallyDropGhostTable && migrationContext.Resurrect {
+		log.Fatalf("--initially-drop-ghost-table and --resurrect are mutually exclusive")
+	}
+	if migrationContext.InitiallyDropOldTable && migrationContext.Resurrect {
+		log.Fatalf("--initially-drop-old-table and --resurrect are mutually exclusive")
+	}
 
 	switch *cutOver {
 	case "atomic", "default", "":

go/logic/migrator.go

@@ -1043,11 +1043,14 @@ func (this *Migrator) executeWriteFuncs() error {
 		case <-contextDumpTick:
 			{
 				this.migrationContext.SetStreamerBinlogCoordinates(this.eventsStreamer.GetCurrentBinlogCoordinates())
+				if !this.migrationContext.Resurrect || this.migrationContext.IsResurrected {
 					if jsonString, err := this.migrationContext.ToJSON(); err == nil {
 						this.applier.WriteChangelog("context", jsonString)
 						log.Debugf("Context dumped")
 					}
 				}
+				// If we're about to resurrect (resurrect requested) but haven't done so yet, do not wrtie resurrect info.
+			}
 		case applyEventFunc := <-this.applyEventsQueue:
 			{
 				if err := this.retryOperation(applyEventFunc); err != nil {