[Gluster-devel] Question on choosing source of replica to heal with AFR

[Ravishankar N]

On 02/26/2014 07:42 PM, Zhang Huan wrote:
> Hello guys,
>
> Anyone know about my question?
>
> Zhang Huan
>
>
> On Sun, Feb 23, 2014 at 11:28 AM, Zhang Huan <zhhuan at gmail.com 
> <mailto:zhhuan at gmail.com>> wrote:
>
>     Hello all,
>
>     While reading codes about how to choose healing source, there is
>     one thing that confuse me. Say we have 3 replica, and 2 of them
>     are OK and the left one is outdated due to temporary IO failure.
>     For some reason, one of the 2 correct replica is truncated to 0
>     due to some underlying correction. Will glusterfs kick the 0 size
>     file out? or still consider it a correct one and may corrupt the
>     left correct replica by healing?
>
Out of the two correct replicas, gluster will pick the first healthy 
replica brick as source [see afr_sh_select_source()]. If that brick is 
truncated at the back-end due to 'underlying correction' (not sure what 
that means), then yes I'm afraid it will still be considered as correct 
source and you would get zero byte file in other 2 bricks because of the 
healing.
>
>     In function afr_mark_sources(), it kicks 0 size file out when all
>     nodes are innocent. Even when all nodes are fools, the file with
>     largest size will be chosen as source. When it comes to the case
>     that there is wise nodes, it won't further check file size.
>     Considering different file size of replicate will trigger healing
>     to work, I am wondering if there is any reason behind the code?
>
The changelog extended attributes are marked  by AFR based on the result 
of whether the file operation succeeded or not on each of the replica. 
It uses those attributes to determine the source/sink. Direct 
modification of the file at the brick will invalidate any meaning that 
the changelog holds.
Thanks,
Ravi
>
>
>     Thanks.
>
>     Zhang Huan
>
>
>
>
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