[Bugs] [Bug 1262415] New: Data Tiering:Scanning files in cold tier when detach tier is issued can take a toll on performance

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1262415

            Bug ID: 1262415
           Summary: Data Tiering:Scanning files in cold tier when detach
                    tier is issued can take a toll on performance
           Product: GlusterFS
           Version: 3.7.4
         Component: tiering
          Severity: high
          Assignee: bugs at gluster.org
          Reporter: nchilaka at redhat.com
        QA Contact: bugs at gluster.org
                CC: bugs at gluster.org



Description of problem:
=======================
I had about 1Lakh files in cold tier and no files in hot tier.
I then issued a detach tier start and check the status.
the status after complete showed as files scanned as all 1Lakh,
Which means if it is rightly showing, we are unncessarily scanning cold tier,
which we must avoid for performance sake.

In below case it can be seen that it took about nearly two minutes for detach
tier to complete, as it had scanned all cold files. In this case it should have
got over in a few seconds as there were no hot files in hot tier.




Version-Release number of selected component (if applicable):
================================================================
[root at zod ~]# rpm -qa|grep gluster
glusterfs-client-xlators-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-cli-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-libs-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-api-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-fuse-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-debuginfo-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-server-3.7.4-0.27.git143f0f9.el7.centos.x86_64
glusterfs-3.7.4-0.27.git143f0f9.el7.centos.x86_64
[root at zod ~]# gluster --version
glusterfs 3.7.4 built on Sep  9 2015 01:30:47
Repository revision: git://git.gluster.com/glusterfs.git
Copyright (c) 2006-2011 Gluster Inc. <http://www.gluster.com>
GlusterFS comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GlusterFS under the terms of the GNU General
Public License.
[root at zod ~]# 



Steps to Reproduce:
==================
1.have a volume and create thousands of files  in cold tier and attach a tier
such
2.now issue a detach tier start and wait for it to complete
3.now check the detach tier status, which will show as complete for each node.
But it can be seen that even without any files in hot tier, the files scanned
will show as number of files in cold tier, which is wrong

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