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https://issues.apache.org/jira/browse/ZOOKEEPER-2789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16027107#comment-16027107
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ASF GitHub Bot commented on ZOOKEEPER-2789:
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Github user asdf2014 commented on the issue:
https://github.com/apache/zookeeper/pull/262
Hi, @maoling. Thanks for your discussion. Maybe due to my description is
problematic, so make you confused.
1. I am worry about if the lower 8 bits of the upper 32 bits are divided
into the low 32 bits of the entire `long` and become 40 bits low, there may be
a concurrent problem. Actually, it shouldn't be worried, all operation about
`ZXID` is bit operation rather than `=` assignment operation. So, it cann't be
a concurrent problem in `JVM` level.
2. Yep, it is. Especially, if it is `1k/s` ops, then as long as $2^{32} /
(86400 * 1000) \approx 49.7$ days `ZXID` will exhausted. And more terrible
situation will make the `re-election` process comes early. At the same time,
the "re-election" process could take half a minute. And it will be cannot
acceptable.
3. As so far, it will throw a `XidRolloverException` to force `re-election`
process and reset the `counter` to zero.
> Reassign `ZXID` for solving 32bit overflow problem
> --------------------------------------------------
>
> Key: ZOOKEEPER-2789
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2789
> Project: ZooKeeper
> Issue Type: Bug
> Components: quorum
> Affects Versions: 3.5.3
> Reporter: Benedict Jin
> Assignee: Benedict Jin
> Fix For: 3.6.0
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> If it is `1k/s` ops, then as long as $2^32 / (86400 * 1000) \approx 49.7$
> days ZXID will exhausted. But, if we reassign the `ZXID` into 16bit for
> `epoch` and 48bit for `counter`, then the problem will not occur until after
> $Math.min(2^16 / 365, 2^48 / (86400 * 1000 * 365)) \approx Math.min(179.6,
> 8925.5) = 179.6$ years.
> However, i thought the ZXID is `long` type, reading and writing the long type
> (and `double` type the same) in JVM, is divided into high 32bit and low 32bit
> part of the operation, and because the `ZXID` variable is not modified with
> `volatile` and is not boxed for the corresponding reference type (`Long` /
> `Double`), so it belongs to [non-atomic operation]
> (https://docs.oracle.com/javase/specs/jls/se8 /html/jls-17.html#jls-17.7).
> Thus, if the lower 32 bits of the upper 32 bits are divided into the entire
> 32 bits of the `long`, there may be a concurrent problem.
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