Mailing-List: contact dev-help@zookeeper.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@zookeeper.apache.org
Date: Tue, 23 May 2017 03:01:04 +0000 (UTC)
From: "ASF GitHub Bot (JIRA)" <jira@apache.org>
To: dev@zookeeper.apache.org
Message-ID: <JIRA.13074069.1495503902000.268824.1495508464210@Atlassian.JIRA>
In-Reply-To: <JIRA.13074069.1495503902000@Atlassian.JIRA>
References: <JIRA.13074069.1495503902000@Atlassian.JIRA> <JIRA.13074069.1495503902442@jira-lw-us.apache.org>
Subject: [jira] [Commented] (ZOOKEEPER-2789) Reassign `ZXID` for solving
 32bit overflow problem
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
archived-at: Tue, 23 May 2017 03:01:10 -0000


    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16020594#comment-16020594 ] 

ASF GitHub Bot commented on ZOOKEEPER-2789:
-------------------------------------------

Github user asdf2014 commented on the issue:

    https://github.com/apache/zookeeper/pull/262
  
    Thinking about some abnormal situations, maybe 24 bit for `epoch` and 40 bit for `counter` is more better choice: $Math.min(2^{24} / (24 * 365), 2^{40} / (86400 * 1000 * 365)) \approx Math.min(1915.2, 34.9) = 34.9$


> 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.


--
This message was sent by Atlassian JIRA
(v6.3.15#6346)