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From asdf2014 <...@git.apache.org>
Subject [GitHub] zookeeper pull request #262: ZOOKEEPER-2789: Reassign `ZXID` for solving 32b...
Date Tue, 23 May 2017 02:04:44 GMT
GitHub user asdf2014 opened a pull request:

    https://github.com/apache/zookeeper/pull/262

    ZOOKEEPER-2789: Reassign `ZXID` for solving 32bit overflow problem

    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.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/asdf2014/zookeeper reassign_zxid

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/zookeeper/pull/262.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #262
    
----
commit 0d7dabb6b6a42f430223c51a1738e03d4d340c79
Author: asdf2014 <1571805553@qq.com>
Date:   2017-05-23T02:02:14Z

    ZOOKEEPER-2789: Reassign `ZXID` for solving 32bit overflow problem

----


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