[Bugs] [Bug 1217381] [RFE] Rebalance Performance Improvements

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1217381



--- Comment #5 from Anand Avati <aavati at redhat.com> ---
COMMIT: http://review.gluster.org/10466 committed in release-3.7 by Vijay
Bellur (vbellur at redhat.com) 
------
commit 579186aeba940e3ec73093c48e17b5f6f94910d0
Author: Susant Palai <spalai at redhat.com>
Date:   Sun Apr 12 15:55:02 2015 +0530

    rebalance: Introducing local crawl and parallel migration

    The current patch address two part of the design proposed.
    1. Rebalance multiple files in parallel
    2. Crawl only bricks that belong to the current node

    Brief design explanation for the above two points.

    1. Rebalance multiple files in parallel:
       -------------------------------------
    The existing rebalance engine is single threaded. Hence, introduced
    multiple threads which will be running parallel to the crawler. The
    current rebalance migration is converted to a "Producer-Consumer"
    frame work.

    Where Producer is : Crawler
          Consumer is : Migrating Threads

    Crawler: Crawler is the main thread. The job of the crawler is now
    limited to fix-layout of each directory and add the files which are
    eligible for the migration to a global queue in a round robin manner
    so that we will use all the disk resources efficiently. Hence, the
    crawler will not be "blocked" by migration process.

    Producer: Producer will monitor the global queue. If any file is
    added to this queue, it will dqueue that entry and migrate the file.
    Currently 20 migration threads are spawned at the beginning of the
    rebalance process. Hence, multiple file migration happens in parallel.

    2. Crawl only bricks that belong to the current node:
       --------------------------------------------------
    As rebalance process is spawned per node, it migrates only the files
    that belongs to it's own node for the sake of load balancing. But it
    also reads entries from the whole cluster, which is not necessary as
    readdir hits other nodes.

    New Design:
            As part of the new design the rebalancer decides the subvols
    that are local to the rebalancer node by checking the node-uuid of
    root directory prior to the crawler starts. Hence, readdir won't hit
    the whole cluster  as it has already the context of local subvols and
    also node-uuid request for each file can be avoided. This makes the
    rebalance process "more scalable".

    Change-Id: I6f1b44086a09df8ca23935fd213509c70cc0c050
    BUG: 1217381
    Signed-off-by: Susant Palai <spalai at redhat.com>
    Reviewed-on: http://review.gluster.org/10466
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Tested-by: NetBSD Build System
    Reviewed-by: N Balachandran <nbalacha at redhat.com>

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