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  1. ZooKeeper
  2. ZOOKEEPER-2789

Reassign `ZXID` for solving 32bit overflow problem

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      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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            • Assignee:
              benedict jin Benedict Jin
              Reporter:
              benedict jin Benedict Jin

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                Estimated:
                Original Estimate - 168h
                168h
                Remaining:
                Remaining Estimate - 167h 40m
                167h 40m
                Logged:
                Remaining Estimate - 167h 40m
                20m

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