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

[Mohit Agrawal]

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.

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
>>
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>>
>
>
>
> --
> Pranith
>
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