fix: use cut-over-lock-timeout for instant DDL

Addresses #1386

by reusing the cut-over-lock-timeout from the cutover code.
The lock wait timeout in the original code is actually set to double
the setting, so we keep that consistent.

Author: artemvovk

go/logic/applier.go

@@ -255,6 +255,15 @@ func (this *Applier) ValidateOrDropExistingTables() error {
 func (this *Applier) AttemptInstantDDL() error {
 	query := this.generateInstantDDLQuery()
 	this.migrationContext.Log.Infof("INSTANT DDL query is: %s", query)
+
+	// Reuse cut-over-lock-timeout from regular migration process to reduce risk
+	// in situations where there may be long-running transactions.
+	tableLockTimeoutSeconds := this.migrationContext.CutOverLockTimeoutSeconds * 2
+	this.migrationContext.Log.Infof("Setting LOCK timeout as %d seconds", tableLockTimeoutSeconds)
+	query = fmt.Sprintf(`set /* gh-ost */ session lock_wait_timeout:=%d`, tableLockTimeoutSeconds)
+	if _, err := this.db.Exec(query); err != nil {
+		return err
+	}
 	// We don't need a trx, because for instant DDL the SQL mode doesn't matter.
 	_, err := this.db.Exec(query)
 	return err