[Gluster-devel] AFR conservative merge portability

[Krutika Dhananjay]

Seems OK to me, as long as the appropriate locks are taken. 

-Krutika 

----- Original Message -----

> From: "Emmanuel Dreyfus" <manu at netbsd.org>
> To: "Gluster Devel" <gluster-devel at gluster.org>
> Sent: Saturday, December 13, 2014 8:08:03 PM
> Subject: [Gluster-devel] AFR conservative merge portability

> Hello

> On NetBSD, tests/basic/afr/entry-self-heal.t always fail on this
> scenario:

> mkdir spb_heal
> kill brick brick0
> touch spb_heal/0
> glusterfs volume start force
> kill_brick brick1
> touch spb_heal/1
> glusterfs volume start force

> At that time, conservative merge takes off and copy spb_heal/0 and
> spb_heal/1 in each brick where it is missing. That works, but on NetBSD
> we are left with AFR xattr on spb_heal directory telling each brick
> accuses the other for metadata. This metadata split brain that will not
> self heal.

> This happens because after adding an entry, parent directory (spb_heal
> here) mtime/ctime must be updated. On Linux, it seems the filesystem is
> responsible for that. On NetBSD, the kernel filesyste-independant code
> takes care of it and will send a SETATTR to update ctime/mtime on parent
> directory.

> So when we touch spb_heal/0 and spb_heal/1, the NetBSD kernel sends a
> SETATTR for spb_heal ctime/mtine, and since the other brick is down,
> here is our metadata split brain.

> In http://review.gluster.org/9267, Krutika Dhananjay fixes the test by
> clearing AFR xattr to remove the split brain state, but while it let the
> test pass, it does not address the real world problem that will leave
> metadata split brain that does not self heal.

> Here is a proposal: we know that at the end of conservative merge, we
> should end up with the situation where directory ctime/mtime is the
> ctime of the most recently added children. And fortunately, as
> conservative merge happens, parent directory ctime/mtime are updated on
> each child addition, and we finish in the desired state.

> In other words, after conservative merge, parent directory metadata
> split brain for only ctime/mtime can just be cleared by AFR without any
> harm.

> Does it looks reasonable? Any opinion?

> --
> Emmanuel Dreyfus
> http://hcpnet.free.fr/pubz
> manu at netbsd.org
> _______________________________________________
> Gluster-devel mailing list
> Gluster-devel at gluster.org
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