mysql relay log大小问题

从库max_relay_log_size 为默认值(1G)，但是relay log文件的大小却不一样，而且是有规律的变化，为什么会这样？参数设置：
MySQL> show variables like '%relay%';
+---------------------------+----------------+
| Variable_name             | Value          |
+---------------------------+----------------+
| max_relay_log_size        | 0              |大小              文件名
536871172 relay-bin.000340
              280 relay-bin.000341
              193 relay-bin.000342
536871093 relay-bin.000343
              280 relay-bin.000344
              193 relay-bin.000345
537182958 relay-bin.000346
              280 relay-bin.000347
              193 relay-bin.000348
536874706 relay-bin.000349
     1841414 relay-bin.000350
              193 relay-bin.000351
536873608 relay-bin.000352
          44116 relay-bin.000353
              193 relay-bin.000354
536874103 relay-bin.000355
          20299 relay-bin.000356
              193 relay-bin.000357
536881344 relay-bin.000358
          57110 relay-bin.000359