[Bugs] [Bug 1292749] Friend update floods can render the cluster incapable of handling other commands

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1292749



--- Comment #3 from Vijay Bellur <vbellur at redhat.com> ---
COMMIT: http://review.gluster.org/12999 committed in master by Atin Mukherjee
(amukherj at redhat.com) 
------
commit f624abd6885752eeaa8d07101ff00f52af48de26
Author: Kaushal M <kaushal at redhat.com>
Date:   Thu Dec 17 11:13:36 2015 +0530

    glusterd: reduce friend update flood

    When in a befriended state, glusterd would broadcast friend updates to
    all other peers whenver a ACC or LOCAL_ACC event occurred.

    When a downed glusterd came back up and established connections again,
    this lead to a flood of friend updates to happen on the order of N^2 (N
    is the number of peers in the cluster)

    In larger clusters this was problematic, and could lead to very long
    times for the cluster to settle down when a peer came back up. Multiple
    peers coming back up at the same time would compound the problem.

    Broadcasting of friend updates doesn't have much use in places other
    that during a peer probe. Instead of broadcasting friend updates on
    connection re-establishment, updates can just be exchanged between the
    peers involved in the connection.

    This patch changes the glusterd friend state-machine to send updates
    only to the required peer for ACC or LOCAL_ACC events when in befriended
    state. The number of updates sent now is in the order of N.

    For a 10 node cluster, the number of updates reduced by 5 times. When
    creating the 10 node cluster, the updates reduced from ~500 to ~150.
    When a glusterd restarted, the number of exchanges reduced from ~160 to
    ~35.

    BUG: 1292749
    Change-Id: Ib6072090c7069b081d018cdaa3dc878819ab1d18
    Signed-off-by: Kaushal M <kaushal at redhat.com>
    Reviewed-on: http://review.gluster.org/12999
    Reviewed-by: Atin Mukherjee <amukherj at redhat.com>
    Tested-by: NetBSD Build System <jenkins at build.gluster.org>
    Tested-by: Gluster Build System <jenkins at build.gluster.com>

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