[Bugs] [Bug 1369638] DHT stale layout issue will be seen often with md-cache prolonged cache of lookups

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1369638



--- Comment #8 from Worker Ant <bugzilla-bot at gluster.org> ---
COMMIT: http://review.gluster.org/15300 committed in master by Raghavendra G
(rgowdapp at redhat.com) 
------
commit 065a27948c4e0651f5bdac1703939adf34e5380e
Author: Poornima G <pgurusid at redhat.com>
Date:   Tue Aug 23 18:15:22 2016 +0530

    dht, md-cache, upcall: Add invalidation of IATT when the layout changes

    Issue:
    dht_layout is built as a part of lookup only. The layout can be
    modified by rebalance process. Since every IO fop is preceded
    by a lookup, there are very less issues of stale layout. But
    with enhancements of aggressive caching of stats in md-cache,
    the lookup will reduce and expose the stale layout issue often.

    Solution:
    Since stale layout is already an issue on dht, there is already
    a plan to fix this at the dht layer, but this fix is not currently
    planned for any release. Until this fix comes out, we can have
    a workaround where, the upcall will send a notification to md-cache
    when a layout xattr is changed. As a part of layout change notification
    the existing cache is invalidated and the next lookup will fetch the
    latest layout.

    This is not a foolproof solution as the window between the layout change
    and the next lookup(after invalidation of stat), where there will be stale
    layout. But until the final fix comes in, this reduces the stale layout
    window.

    Change-Id: Iacf871a38b35880c1fc0bc68fe7ce291265e71d4
    BUG: 1369638
    Signed-off-by: Poornima G <pgurusid at redhat.com>
    Reviewed-on: http://review.gluster.org/15300
    NetBSD-regression: NetBSD Build System <jenkins at build.gluster.org>
    CentOS-regression: Gluster Build System <jenkins at build.gluster.org>
    Smoke: Gluster Build System <jenkins at build.gluster.org>
    Reviewed-by: Raghavendra G <rgowdapp at redhat.com>

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