Re: OSD abstract class

[Loic Dachary <loic@dachary.org>]

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On 04/25/2013 06:45 PM, Gregory Farnum wrote:
> On Thu, Apr 25, 2013 at 1:17 AM, Loic Dachary <loic@dachary.org> wrote:
>> Hi,
>>
>> In the context of the implementation of
>>
>> http://wiki.ceph.com/01Planning/02Blueprints/Dumpling/Erasure_encoding_as_a_storage_backend
>>
>> I'm preparing tests to assert that the modifications that will be made to the existing PG and ReplicatedPG will not introduce regressions. Unless I'm mistaken, there are no unit tests or functional tests for PG or ReplicatedPG at the moment. I thought that it might be useful to add an abstract OSD class from which OSD is derived, to allow a test to derive from it to implement synthetic behavior.
>>
>>
>> I gave it a try and it passes make check successfully. It is a little hairy because I commented out the code instead of removing it to help with rebasing.
>>
>> https://github.com/dachary/ceph/commit/a9eb690a3537c3f844b47e76cde048b084e314eb
>>
>> I'll now try to use it to implement some tests for ReplicatedPG.
>>
>> I would very much appreciate if someone has an advice on the best way to proceed. Even if it's to say : "you're crazy, don't go there ! you're wasting your time, there is a much simpler way !" ;-)
> 
> What's your plot here? The OSD is fairly large to be doing unit tests
> on (although it's not insensible) — but if we want to form a new PG it
> might be best to start out by making abstract PG implementations.
> 

My reasoning was that to for a new PG it was enough to rely on

https://github.com/ceph/ceph/blob/master/src/osd/PG.h

and create a new ErasureEncodingPG.{cc,h} after 

https://github.com/ceph/ceph/blob/master/src/osd/ReplicatedPG.cc

Since ReplicatedPG is the only class derived from PG, I assumed there will be a need to move code from ReplicatedPG to PG and vice versa to make sure PG can actually be the base class of two different implementations. Are you suggesting that PG should be abstracted ? Is there a reason why it would not be a good base class for a new ErasureEncodedPG ? 

> That'll be a bit easier since I believe I they only access the
> OSDService now, and not the OSD proper.

Indeed :-) It will be a lot easier to write an OSDService abstract class to be derived for test purposes. It is much more complicated to do the same with OSD. And probably not necessary since PG's only access OSD thru OSDService. 

Thanks a thousand time for the tip :-)

> -Greg
> Software Engineer #42 @ http://inktank.com | http://ceph.com
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-- 
Loïc Dachary, Artisan Logiciel Libre


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