[ https://issues.apache.org/jira/browse/ZOOKEEPER2789?page=com.atlassian.jira.plugin.system.issuetabpanels:alltabpanel
]
Benedict Jin updated ZOOKEEPER2789:

Description:
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 [nonatomic operation] (https://docs.oracle.com/javase/specs/jls/se8
/html/jls17.html#jls17.7). 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.
was:
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 [nonatomic operation] (https://docs.oracle.com/javase/specs/jls/se8
/html/jls17.html#jls17.7). 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.
> Reassign `ZXID` for solving 32bit overflow problem
> 
>
> Key: ZOOKEEPER2789
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER2789
> Project: ZooKeeper
> Issue Type: Bug
> Components: quorum
> Affects Versions: 3.5.3
> Reporter: 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 [nonatomic operation] (https://docs.oracle.com/javase/specs/jls/se8
/html/jls17.html#jls17.7). 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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