[Bugs] [Bug 1217944] Changelog: Changelog should be treated as discontinuous only on changelog enable/disable

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1217944



--- Comment #3 from Anand Avati <aavati at redhat.com> ---
COMMIT: http://review.gluster.org/10507 committed in release-3.7 by Vijay
Bellur (vbellur at redhat.com) 
------
commit baac2c28ee98e47a3fc0ecf1db3779c7372df526
Author: Kotresh HR <khiremat at redhat.com>
Date:   Mon Apr 13 20:28:21 2015 +0530

    features/changelog: Consider only changelog on/off as changelog breakage

    Earlier, both chagelog on/off and brick restart were considered
    to be changelog breakage and treated as changelog not being
    continuous. As a result, new HTIME.TSTAMP file was created on
    both the above cases. Now the change is made such that only
    on changelog enable/disable, the changelog is considered to be
    discontinuous. New HTIME.TSTAMP file is not created on brick
    restart, the changelogs files are appended to last HTIME.TSTAMP
    file.

    Treating changelog as continuous in above scenario is important
    as changelog history API will fail otherwise. It can successfully
    get changes between start and end timestamps only when changelog
    is continuous (Changelogs in single HTIME.TSTAMP file are treated
    as continuous). Without this change, changelog history API would
    fail, and it would become necessary to fallback to other mechanisms
    like xsync FSCrawl in case geo-rep to detect changes in this time
    window. But Xsync FSCrawl would not be applicable to other
    consumers like glusterfind.

    Rationale:
    1. In plain distributed volume, if brick goes down, no I/O can
       happen onto the brick. Hence changelog is intact with data
       on disk.
    2. In distributed replicate volume, if brick goes down, since
       self-heal traffic is captured in changelog. Eventually,
       I/O happened whend brick down is captured in changelog.

    BUG: 1217944
    Change-Id: Ifa6d932818fe1a3a914e87ac84f1d2ded01c1288
    Signed-off-by: Kotresh HR <khiremat at redhat.com>
    Reviewed-on: http://review.gluster.org/10222
    Reviewed-on: http://review.gluster.org/10507
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Reviewed-by: Aravinda VK <avishwan at redhat.com>
    Reviewed-by: Vijay Bellur <vbellur at redhat.com>

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