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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2789) Reassign `ZXID` for solving 32bit overflow problem
Date Tue, 23 May 2017 05:12:04 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16020672#comment-16020672
] 

Hadoop QA commented on ZOOKEEPER-2789:
--------------------------------------

-1 overall.  GitHub Pull Request  Build
      

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 15 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 3.0.1) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit
warnings.

    -1 core tests.  The patch failed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/738//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/738//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/738//console

This message is automatically generated.

> 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
>
>   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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