[Gluster-devel] Readdir plus implementation in tier xlator

[Vijay Bellur]

On Fri, Apr 22, 2016 at 1:46 AM, Mohammed Rafi K C <rkavunga at redhat.com> wrote:
> comments are inline.
>
> On 04/22/2016 09:41 AM, Vijay Bellur wrote:
>> On Mon, Apr 18, 2016 at 3:28 AM, Mohammed Rafi K C <rkavunga at redhat.com> wrote:
>>> But the problem comes when we use gf_api, where we don't have any
>>> control over client behavior. So to fix this issue we have to give stat
>>> information for all the entries.
>>>
>> Apart from Samba, what other consumers of gfapi have this problem?
>
> In nfs-ganesha, What I understand is, they are not sending readdirp. So
> there we are good. But any other app which always expect a valid
> response from readdirp will fail.


For such consumers that need strict readdirplus from tiering, we can
make this behavior optional. Exposing a tunable that can be either set
by the administrators for the volume that the consumer acts on or
letting the application invoke glfs_set_xlator_option() would be nice.


>>
>>
>>> 4. Revert to dht_readdirp and then instead of taking all entries from
>>> hot tier, just take only entries which has T file in cold tier. (We can
>>> delay deleting of data file after demotion, so that we will get the stat
>>> from hot tier)
>>>
>> Going by the architectural model of xlators, tier should provide the
>> right entries with attributes to the upper layers (xlators/vfs etc.).
>> Relying on a specific behavior from layers above us to mask a problem
>> in our layer does not seem ideal.  I would go with something like 2 or
>> 3.  If we want to retain the current behavior, we should make it
>> conditional as I am not certain that this behavior is foolproof too.
>
> If we make the changes in tier_readdirp, then it effects the performance
> of plane readdir (if md-cache was on). we may need to  turn off volume
> option "performance.force-readdirp". What do you think here ?
>

If we make the behavior optional as I describe above, then tier would
not have to impact performance in readdir/readdirplus for accesses
through fuse/NFS etc and let the current behavior remain.

Regards,
Vijay