Benedict Jin created ZOOKEEPER-2789:
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Summary: 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
Fix For: 3.6.0
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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