Merge pull request github#1141 from shaohk/fix-two-phase-commit-lost-data_v2

fix(lost data in mysql two-phase commit): lost data in mysql two-phas…

Author: dm-2

go/logic/applier.go

@@ -424,8 +424,28 @@ func (this *Applier) ReadMigrationMaxValues(uniqueKey *sql.UniqueKey) error {
 	return err
 }
 
-// ReadMigrationRangeValues reads min/max values that will be used for rowcopy
+// ReadMigrationRangeValues reads min/max values that will be used for rowcopy.
+// Before read min/max, write a changelog state into the ghc table to avoid lost data in mysql two-phase commit.
+/*
+Detail description of the lost data in mysql two-phase commit issue by @Fanduzi:
+	When using semi-sync and setting rpl_semi_sync_master_wait_point=AFTER_SYNC,
+	if an INSERT statement is being committed but blocks due to an unmet ack count,
+	the data inserted by the transaction is not visible to ReadMigrationRangeValues,
+	so the copy of the existing data in the table does not include the new row inserted by the transaction.
+	However, the binlog event for the transaction is already written to the binlog,
+	so the addDMLEventsListener only captures the binlog event after the transaction,
+	and thus the transaction's binlog event is not captured, resulting in data loss.
+
+	If write a changelog into ghc table before ReadMigrationRangeValues, and the transaction commit blocks
+	because the ack is not met, then the changelog will not be able to write, so the ReadMigrationRangeValues
+	will not be run. When the changelog writes successfully, the ReadMigrationRangeValues will read the
+	newly inserted data, thus Avoiding data loss due to the above problem.
+*/
 func (this *Applier) ReadMigrationRangeValues() error {
+	if _, err := this.WriteChangelogState(string(ReadMigrationRangeValues)); err != nil {
+		return err
+	}
+
 	if err := this.ReadMigrationMinValues(this.migrationContext.UniqueKey); err != nil {
 		return err
 	}

go/logic/migrator.go

@@ -26,6 +26,7 @@ type ChangelogState string
 const (
 	GhostTableMigrated         ChangelogState = "GhostTableMigrated"
 	AllEventsUpToLockProcessed                = "AllEventsUpToLockProcessed"
+	ReadMigrationRangeValues                  = "ReadMigrationRangeValues"
 )
 
 func ReadChangelogState(s string) ChangelogState {
@@ -236,6 +237,8 @@ func (this *Migrator) onChangelogStateEvent(dmlEvent *binlog.BinlogDMLEvent) (er
 				this.applyEventsQueue <- newApplyEventStructByFunc(&applyEventFunc)
 			}()
 		}
+	case ReadMigrationRangeValues:
+		// no-op event
 	default:
 		{
 			return fmt.Errorf("Unknown changelog state: %+v", changelogState)