[Gluster-devel] Query regards to heal xattr heal in dht

[Pranith Kumar Karampuri]

On Wed, Sep 7, 2016 at 9:46 PM, Mohit Agrawal <moagrawa at redhat.com> wrote:

> Hi Pranith,
>
>
> In current approach i am getting list of xattr from first up volume and
> update the user attributes from that xattr to
> all other volumes.
>
> I have assumed first up subvol is source and rest of them are sink as we
> are doing same in dht_dir_attr_heal.
>

I think first up subvol is different for different mounts as per my
understanding, I could be wrong.


>
> Regards
> Mohit Agrawal
>
> On Wed, Sep 7, 2016 at 9:34 PM, Pranith Kumar Karampuri <
> pkarampu at redhat.com> wrote:
>
>> hi Mohit,
>>        How does dht find which subvolume has the correct list of xattrs?
>> i.e. how does it determine which subvolume is source and which is sink?
>>
>> On Wed, Sep 7, 2016 at 2:35 PM, Mohit Agrawal <moagrawa at redhat.com>
>> wrote:
>>
>>> Hi,
>>>
>>>   I am trying to find out solution of one problem in dht specific to
>>> user xattr healing.
>>>   I tried to correct it in a same way as we are doing for healing dir
>>> attribute but i feel it is not best solution.
>>>
>>>   To find a right way to heal xattr i want to discuss with you if anyone
>>> does have better solution to correct it.
>>>
>>>   Problem:
>>>    In a distributed volume environment custom extended attribute value
>>> for a directory does not display correct value after stop/start the brick.
>>> If any extended attribute value is set for a directory after stop the brick
>>> the attribute value is not updated on brick after start the brick.
>>>
>>>   Current approach:
>>>     1) function set_user_xattr to store user extended attribute in
>>> dictionary
>>>     2) function dht_dir_xattr_heal call syncop_setxattr to update the
>>> attribute on all volume
>>>     3) Call the function (dht_dir_xattr_heal) for every directory lookup
>>> in dht_lookup_revalidate_cbk
>>>
>>>   Psuedocode for function dht_dir_xatt_heal is like below
>>>
>>>    1) First it will fetch atttributes from first up volume and store
>>> into xattr.
>>>    2) Run loop on all subvolume and fetch existing attributes from every
>>> volume
>>>    3) Replace user attributes from current attributes with xattr user
>>> attributes
>>>    4) Set latest extended attributes(current + old user attributes) inot
>>> subvol.
>>>
>>>
>>>    In this current approach problem is
>>>
>>>    1) it will call heal function(dht_dir_xattr_heal) for every directory
>>> lookup without comparing xattr.
>>>     2) The function internally call syncop xattr for every subvolume
>>> that would be a expensive operation.
>>>
>>>    I have one another way like below to correct it but again in this one
>>> it does have dependency on time (not sure time is synch on all bricks or
>>> not)
>>>
>>>    1) At the time of set extended attribute(setxattr) change time in
>>> metadata at server side
>>>    2) Compare change time before call healing function in
>>> dht_revalidate_cbk
>>>
>>>     Please share your input on this.
>>>     Appreciate your input.
>>>
>>> Regards
>>> Mohit Agrawal
>>>
>>> _______________________________________________
>>> Gluster-devel mailing list
>>> Gluster-devel at gluster.org
>>> http://www.gluster.org/mailman/listinfo/gluster-devel
>>>
>>
>>
>>
>> --
>> Pranith
>>
>
>


-- 
Pranith
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