zookeeper选举的zxid的疑问

Question

zk的每一个事务都会有一个唯一的事务id，这个id是一个64位的整数。前32位是逻辑时钟号，后32位是某个逻辑时钟下的单调递增的id，我的疑问是如果在一个任期内（前32位不变），后面的32位用尽了那么整个集群会怎么办？是重新选leader？还是leader不变然后将前32位加1后32位从0开始自增？如果前32位都用尽了又该怎么办？

Answer 1

int 溢出了你说会发生啥？从 0 开始了呗……

然后会触发 XidRolloverException 异常，重新选举。

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P.S. 相关源码

public Proposal Leader#propose(Request request) throws XidRolloverException {
    /**
    * Address the rollover issue. All lower 32bits set indicate a new leader
    * election. Force a re-election instead. See ZOOKEEPER-1277
    */
    if ((request.zxid & 0xffffffffL) == 0xffffffffL) {
        String msg = "zxid lower 32 bits have rolled over, forcing re-election, and therefore new epoch start";
        shutdown(msg);
        throw new XidRolloverException(msg);
    }
}