+++ This bug was initially created as a clone of Bug #1170913 +++

Description of problem:

The reason self-heal daemons first acquire full locks in self-heal domain in AFR-V2, is to ensure that only one of them gets to enter the critical section and do the healing of a file/directory.

Although this was being achieved before AFR-V2 by way of holding full locks in xlator domain (the domain where normal modification FOPs take locks in the clients' I/O path) until the given file/directory is healed, the disadvantage with this approach was that the clients in the normal I/O path would be required to wait until this file/dir is healed, and in cases where the to-be-healed files are really large (think VM images), the clients would perceive a hung file system with nothing working.

Therefore, to eliminate this, self-heal domain locks were introduced exclusively for use by self-heal daemon.

However, metadata self-heal is a relatively fast operation (irrespective of how big the file/directory is). Hence, it can possibly eliminate locking in sh-domain and directly proceed with a blocking locks acquisition in xlator domain, perform metadata healing (a bunch of getxattrs, setxattrs, removexattrs and setattr), and a quick unlock on the held locks.

This way,
a. No two healers can concurrently perform metadata healing of a file/dir;
b. The clients themselves cannot enter the critical section either to modify metadata while selfheal is in progress.
c. The clients in the normal i/o path do not have to be blocked for a really long time to do metadata FOPs;

Version-Release number of selected component (if applicable):


How reproducible:
N/A

Steps to Reproduce:
1.
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Actual results:


Expected results:


Additional info:

--- Additional comment from Anand Avati on 2014-12-05 01:15:18 EST ---

REVIEW: http://review.gluster.org/9240 (cluster/afr: Eliminate locking in sh domain in metadata self-heal) posted (#1) for review on master by Krutika Dhananjay (kdhananj)

--- Additional comment from Anand Avati on 2014-12-05 04:51:19 EST ---

COMMIT: http://review.gluster.org/9240 committed in master by Pranith Kumar Karampuri (pkarampu) 
------
commit 5fdffa7164ffc5a798246411d065259b36658bc3
Author: Krutika Dhananjay <kdhananj>
Date:   Fri Dec 5 11:16:07 2014 +0530

    cluster/afr: Eliminate locking in sh domain in metadata self-heal
    
    Change-Id: I9ef25a17c9a43ba06fac2ad3f7c18cb47de91537
    BUG: 1170913
    Signed-off-by: Krutika Dhananjay <kdhananj>
    Reviewed-on: http://review.gluster.org/9240
    Tested-by: Gluster Build System <jenkins.com>
    Reviewed-by: Pranith Kumar Karampuri <pkarampu>
    Tested-by: Pranith Kumar Karampuri <pkarampu>