[GitHub] zookeeper pull request #688: reduce session revalidation time after zxid rol...

[TyqITstudent]

GitHub user TyqITstudent opened a pull request:

    https://github.com/apache/zookeeper/pull/688

    reduce session revalidation time after zxid roll over

    **Problem:**
    1. Sometimes Zookeeper cluster will receive a lot of connections from 
clients, sometimes connection number even exceeds 1W. When zxid rolls over, the 
clients will reconnect and revalidate the session.
    2. In Zookeeper design structure, when follower server receives the session 
revalidation requests, it will send requests to leader server, which is 
designed to be responsible for session revalidation.
    3. In a short time, Leader will handle lots of requests. I use a tool to 
get the statistics, some clients need to wait over 20s. It is too long for some 
special clients, like ResourceManager.
    
    **Solution:**
    1. When zookeeper cluster finishes reelection(which will cost a few 
seconds). The leader will send the time point TimeA to followers. （which is 
the approximate value of roll over）
    2. Followers can judge the most session revalidations. When the timeout of 
the session is less than currentTime - timeA , follower will put the session on 
the touchTable. （Every half tickTime, followers will send sessions of 
touchTable to leader to validate）.
    3. When the timeout of the session is larger than currentTime - timeA, the 
follower will send session revalidation request to leader right away.
    
    So the leader will receive fewer requests from followers.

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

    $ git pull https://github.com/TyqITstudent/zookeeper ZOOKEEPER-3169

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

    https://github.com/apache/zookeeper/pull/688.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 #688
    
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commit 6a1aca3de5585325c9b4fb595813fb0f86d5a2ea
Author: 田毅群 <tianyiqun@...>
Date:   2018-11-04T08:45:53Z

    reduce session revalidation time after zxid roll over

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