refine usage of MaxReconnectAttempts in BinlogSyncer (#417)

* refine usage of MaxReconnectAttempts in BinlogSyncer

Author: amyangfei

replication/binlogsyncer.go

@@ -83,9 +83,13 @@ type BinlogSyncerConfig struct {
 	// read timeout
 	ReadTimeout time.Duration
 
-	// maximum number of attempts to re-establish a broken connection
+	// maximum number of attempts to re-establish a broken connection, zero or negative number means infinite retry.
+	// this configuration will not work if DisableRetrySync is true
 	MaxReconnectAttempts int
 
+	// whether disable re-sync for broken connection
+	DisableRetrySync bool
+
 	// Only works when MySQL/MariaDB variable binlog_checksum=CRC32.
 	// For MySQL, binlog_checksum was introduced since 5.6.2, but CRC32 was set as default value since 5.6.6 .
 	// https://dev.mysql.com/doc/refman/5.6/en/replication-options-binary-log.html#option_mysqld_binlog-checksum
@@ -645,6 +649,12 @@ func (b *BinlogSyncer) onStream(s *BinlogStreamer) {
 				return
 			}
 
+			if b.cfg.DisableRetrySync {
+				log.Warn("retry sync is disabled")
+				s.closeWithError(err)
+				return
+			}
+
 			for {
 				select {
 				case <-b.ctx.Done():