[Bugs] [Bug 1262884] New: Data Tiering:Clear/delete database after(or as part of final step) detaching of hot tier to avoid persistant storage wastage

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1262884

            Bug ID: 1262884
           Summary: Data Tiering:Clear/delete database after(or as part of
                    final step) detaching of hot tier to avoid persistant
                    storage wastage
           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:
=======================
We are currently saving the heat patterns of files on database which is stored
in persistant brick memory. In a case where we have say lakhs of cold files and
are ready to get promoted, then these files are marked in the db. Now when a
user issues a detach tier successfuly and detaches the tier , the db still
remains on cold tier bricks. We need to clean this cold bricks to facilitate
proper storage savings, else this can result in large disk space wasted(incase
of huge number of inodes)

Version-Release number of selected component (if applicable):
============================================================
[root at zod ~]# rpm -qa|grep gluster
glusterfs-client-xlators-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-api-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-fuse-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-debuginfo-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-server-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-cli-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
glusterfs-libs-3.7.4-0.33.git1d02d4b.el7.centos.x86_64
[root at zod ~]# gluster --version
glusterfs 3.7.4 built on Sep 12 2015 01:35:35
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.create a tiered volume
2.now have some files in cold tier and heat them such that they are to be
promoted next.
3. Now note down the db size of each brick (eg: du -sh
<brick_path>/.glusterfs/<brick_name>.db)
3.Now detach tier completely (start and commit)
4. Now check the db file and size in cold bricks.
It can be noted that the db still exists and can occupy lot of space when there
are lot of files. This db is of no use on  a regular volume. 



Expected results:
=====================
delete db from a volume where tier has been detached

For Eg:a 1000 file db took about 160KB, then for a 1Million file in this case
can take about 160-300MB atleast which is significant

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