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

[Pranith Kumar Karampuri]

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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