canal client need do connector.rollback() when catching exception

[hxy91819]

• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

environment

• canal version = 1.1.4
• mysql version = 5.7

Issue Description

I have been continuing suffering a data loss when using canal. I found there always been some exceptions (like connect problems) happened with data loss.

So I check the client code in AbstractCanalClientTest.java

In line 79, we got // connector.rollback(batchId); // 处理失败, 回滚数据

I think it will be good if we add connector.rollback(batchId) when we got an exception.

Such as:

while (running) {
    Message message = connector.getWithoutAck(batchSize); // 获取指定数量的数据
    long batchId = message.getId();
    try {
        int size = message.getEntries().size();
        if (batchId == -1 || size == 0) {
            // 无效信息，可以考虑休眠
        } else {
            printSummary(message, batchId, size);
            printEntry(message.getEntries());
            if (handleEntry != null) {
                handleEntry.invoke(message.getEntries());
            }
        }

        if (batchId != -1) {
            connector.ack(batchId); // 提交确认
        }
    } catch (Exception e) {
        try {
            Thread.sleep(1000L);
        } catch (InterruptedException e1) {
            Thread.currentThread().interrupt();
        }
        if (batchId != -1) {
            connector.rollback(batchId); // 处理失败, 回滚数据
        }
    }
}

The question is : why you guys didn't do this in the code of examples? Is this irregular?

Steps to reproduce

Expected behaviour

Actual behaviour

If there is an exception, please attach the exception trace:

Just put your stack trace here!

[agapple]

默认rollbackOnConnect=true，会在下一轮自动rollback，不过代码的确是可以优化一下