Merge pull request #376 from github/old-table-name-timestamp

supporting --timestamp-old-table

Author: Shlomi Noach

doc/command-line-flags.md

@@ -130,3 +130,7 @@ See `approve-renamed-columns`
 ### test-on-replica
 
 Issue the migration on a replica; do not modify data on master. Useful for validating, testing and benchmarking. See [testing-on-replica](testing-on-replica.md)
+
+### timestamp-old-table
+
+Makes the _old_ table include a timestamp value. The _old_ table is what the original table is renamed to at the end of a successful migration. For example, if the table is `gh_ost_test`, then the _old_ table would normally be `_gh_ost_test_del`. With `--timestamp-old-table` it would be, for example, `_gh_ost_test_20170221103147_del`.

go/base/context.go

@@ -121,6 +121,7 @@ type MigrationContext struct {
 	OkToDropTable                bool
 	InitiallyDropOldTable        bool
 	InitiallyDropGhostTable      bool
+	TimestampOldTable            bool // Should old table name include a timestamp
 	CutOverType                  CutOver
 	ReplicaServerId              uint
 
@@ -234,11 +235,12 @@ func (this *MigrationContext) GetGhostTableName() string {
 
 // GetOldTableName generates the name of the "old" table, into which the original table is renamed.
 func (this *MigrationContext) GetOldTableName() string {
-	if this.TestOnReplica {
-		return fmt.Sprintf("_%s_ght", this.OriginalTableName)
-	}
-	if this.MigrateOnReplica {
-		return fmt.Sprintf("_%s_ghr", this.OriginalTableName)
+	if this.TimestampOldTable {
+		t := this.StartTime
+		timestamp := fmt.Sprintf("%d%02d%02d%02d%02d%02d",
+			t.Year(), t.Month(), t.Day(),
+			t.Hour(), t.Minute(), t.Second())
+		return fmt.Sprintf("_%s_%s_del", this.OriginalTableName, timestamp)
 	}
 	return fmt.Sprintf("_%s_del", this.OriginalTableName)
 }

go/cmd/gh-ost/main.go

@@ -77,6 +77,7 @@ func main() {
 	flag.BoolVar(&migrationContext.OkToDropTable, "ok-to-drop-table", false, "Shall the tool drop the old table at end of operation. DROPping tables can be a long locking operation, which is why I'm not doing it by default. I'm an online tool, yes?")
 	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")
+	flag.BoolVar(&migrationContext.TimestampOldTable, "timestamp-old-table", false, "Use a timestamp in old table name. This makes old table names unique and non conflicting cross migrations")
 	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")
 

go/logic/applier.go

@@ -142,6 +142,10 @@ func (this *Applier) ValidateOrDropExistingTables() error {
 			return err
 		}
 	}
+	if len(this.migrationContext.GetOldTableName()) > mysql.MaxTableNameLength {
+		log.Fatalf("--timestamp-old-table defined, but resulting table name (%s) is too long (only %d characters allowed)", this.migrationContext.GetOldTableName(), mysql.MaxTableNameLength)
+	}
+
 	if this.tableExists(this.migrationContext.GetOldTableName()) {
 		return fmt.Errorf("Table %s already exists. Panicking. Use --initially-drop-old-table to force dropping it, though I really prefer that you drop it or rename it away", sql.EscapeName(this.migrationContext.GetOldTableName()))
 	}

go/mysql/utils.go

@@ -16,6 +16,8 @@ import (
 	"github.com/outbrain/golib/sqlutils"
 )
 
+const MaxTableNameLength = 64
+
 type ReplicationLagResult struct {
 	Key InstanceKey
 	Lag time.Duration