I understood. Thanks!
On Wed, Jan 4, 2017 at 10:34 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
> The loop isn't that big of a deal -- but you could eliminate it
> entirely if you just index the in-memory snapshot table via the
> SnapshotNamespace variant instead of just indexing snapshots by name
> (e.g. ImageCtx::snap_ids key switches from a string to a namespace).
> This would be required anyway since you might otherwise have duplicate
> names between namespaces.
>
> On Wed, Jan 4, 2017 at 1:29 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>> It looks like next CDM is only next month. Let's try to figure it out in email.
>>
>>> Since you know which images are linked to the group and you know which
>>> snapshots are in the group and which group snapshots are in the image,
>>> you can reconcile any issues using the details in the
>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>> actual snapshot name (it could technically just be a randomly assigned
>>> UUID).
>>
>> Let's say I have a consistency group and a snapshot of this group: CG
>> and CGSNAP.
>> Images in this snapshot I'll define as:
>> CG.images[0] - image1
>> CG.images[1] - image2
>> CG.images[2] - image3
>>
>> Image snapshots in cg snapshot will be:
>> CG.CGSNAP.snaps[0] - reference to snapshot of image 1
>> CG.CGSNAP.snaps[1] - reference to snapshot of image 2
>>
>> Imagine that this snapshot was created, but wasn't finalized.
>> CG.CGSNAP.state == PENDING.
>> CG.CGSNAP.snaps.length == 0;
>> I'll be writing in pseudo code.
>>
>> Now, let's say we want to remove this pending CGSNAP. This is the code
>> how it's currently implemented:
>>
>> for (image: CG.images) {
>> snap_name = image.id + "_" + CG.CGSNAP.id + "_" + CG.id // This name
>> is unique because of uniqueness of the tuple (image.id, CG.CGSNAP.id,
>> CG.id)
>> remove_image_snapshot(snap_name);
>> }
>> remove_cg_snap(CGSNAP);
>>
>> However, if we don't rely on the name then this is how I envision the code:
>>
>> for (image: CG.images) {
>> for (snap: image.snaps) {
>> if (snap.namespace.cg_id == CG.id && snap.namespace.cg_snap_id ==
>> CG.CGSNAP.id) { // this is our snapshot
>> remove_image_snapshot(snap.name);
>> }
>> }
>> }
>> remove_cg_snap(CGSNAP);
>>
>> In this solution I don't like the internal loop.
>> What do you think?
>>
>> Thanks,
>> Victor.
>>
>>
>> On Tue, Jan 3, 2017 at 6:56 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>> After starting the process of creating a group snapshot, you will
>>> already have all the necessary data for the group snapshot namespace
>>> [1] (group pool, group id, and group snapshot id) and the group
>>> snapshot should be persistently recorded to disk as
>>> GROUP_SNAPSHOT_STATE_PENDING.
>>>
>>> Looking at the snapshot create state machine [2], I don't see any
>>> place that a crash (or similar failure) would matter before the actual
>>> image snapshot record is created atomically. You would pass the fully
>>> populated GroupSnapshotNamespace to snap_create, and if the snapshot
>>> is created, it's linked to the group via that namespace and any
>>> failures afterwards don't matter since they are linked -- if the
>>> snapshot fails to be created, it isn't linked to the group but the
>>> snapshot doesn't exist either so there isn't anything to clean up.
>>>
>>> Since you know which images are linked to the group and you know which
>>> snapshots are in the group and which group snapshots are in the image,
>>> you can reconcile any issues using the details in the
>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>> actual snapshot name (it could technically just be a randomly assigned
>>> UUID).
>>>
>>> Perhaps we could talk about this at a future RBD standup meeting that
>>> you are able to join (or the next CDM).
>>>
>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L249
>>> [2] https://github.com/ceph/ceph/blob/master/src/librbd/operation/SnapshotCreateRequest.h#L28
>>>
>>> On Tue, Jan 3, 2017 at 7:40 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>> Let's say we start creating a group snapshot.
>>>> We invoke async snap_create method in Operations class.
>>>> When we invoke this method we provide it with the snapshot name.
>>>>
>>>> While we are wating for the response we can be aborted.
>>>> As a result we will be able to find the exact image snapshot using only its name
>>>> as this was the only information we had at the time of running
>>>> snap_create method.
>>>>
>>>> If snap_create was successful we will be able to find the snapshot
>>>> otherwise we will not.
>>>> However if we allow renaming snapshots from GroupSnapshotNamespace
>>>> then we may not find the snapshot even if it
>>>> was created successfully.
>>>>
>>>> On Fri, Dec 16, 2016 at 6:53 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>> Can you give a little background on this specific inconsistent case
>>>>> you are referring to?
>>>>>
>>>>> On Thu, Dec 15, 2016 at 7:05 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>> Yes, but if image's snapshot is renamed then I'm not able to find this
>>>>>> snapshot having only group's snapshot in an inconsistent state for
>>>>>> example.
>>>>>>
>>>>>> V.
>>>>>>
>>>>>> On Thu, Dec 15, 2016 at 7:10 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>> I think I might be confused. When creating a group snapshot, we have
>>>>>>> the ConsistencyGroupSnapshot that allows you to store the necessary
>>>>>>> linkage between the image's snapshot and its associated group snapshot
>>>>>>> [1]. Why not just name the image's snapshots to the same name as the
>>>>>>> parent group snapshot name and search the snapshot's metadata to get
>>>>>>> the linkage?
>>>>>>>
>>>>>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L255
>>>>>>>
>>>>>>> On Tue, Dec 13, 2016 at 8:03 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>> Jason,
>>>>>>>>
>>>>>>>> My current implementation of consistency group snapshot feature names
>>>>>>>> image snapshots like: <group_pool>_<group_id>_<group_snap_id>
>>>>>>>> I rely on this fact when I need to remove a consistency group. It's
>>>>>>>> necessary because if some of image snapshots were created, but the
>>>>>>>> whole group snapshot operation failed,
>>>>>>>> then the only way to find those dangling image snapshots is by this name.
>>>>>>>>
>>>>>>>> It means that we should forbid renaming snapshots from
>>>>>>>> ConsistencyGroupSnapshot namespace.
>>>>>>>>
>>>>>>>> Another option is to allocate image snapshot ids during the creation
>>>>>>>> of group snapshot, but this requires a major rewrite of the whole
>>>>>>>> process of snapshot creation for images.
>>>>>>>>
>>>>>>>> What is your opinion on this?
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> V.
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Nov 1, 2016 at 8:01 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>> I chatted with Xing on IRC this morning re: Cinder generic groups. It
>>>>>>>>> sounds like RBD will need to support preserving the image's
>>>>>>>>> consistency group snapshots even if the image is removed from the
>>>>>>>>> group. In the OpenStack case, you won't have to worry about the image
>>>>>>>>> being deleted while it still has associated group snapshots.
>>>>>>>>>
>>>>>>>>> We will also want to support being able to clone child images from a
>>>>>>>>> group snapshot to ensure that we can thin provision new groups volumes
>>>>>>>>> when creating a new group from a group snapshot. This means that the
>>>>>>>>> group snapshots should be able to be protected/unprotected just like
>>>>>>>>> standard user snapshots.
>>>>>>>>>
>>>>>>>>> On Mon, Oct 31, 2016 at 9:07 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>> Looking at the Cinder codebase, I don't see any such restriction that
>>>>>>>>>> would prevent you from removing a volume from a consistency group that
>>>>>>>>>> has associated snapshots. I would double-check on the OpenStack
>>>>>>>>>> development mailing list if this is correct and is the intent. Worst
>>>>>>>>>> case, the RBD driver could raise an exception if there are still
>>>>>>>>>> consistency group snapshots associated to the image.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Fri, Oct 28, 2016 at 6:41 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>> Another thing that bothers me. When we remove an image from a consistency group.
>>>>>>>>>>> Should we remove all snapshots of this image that were created as part
>>>>>>>>>>> of a consistency group snapshot?
>>>>>>>>>>>
>>>>>>>>>>> The easiest solution would be to remove all snapshots that are in
>>>>>>>>>>> GroupSnapshotNamespace and reference this consistency group.
>>>>>>>>>>> I looked into cinder docs for this feature:
>>>>>>>>>>> http://docs.openstack.org/admin-guide/blockstorage-consistency-groups.html
>>>>>>>>>>>
>>>>>>>>>>> But it's not clear to me which behavior cinder expects.
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> V.
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Oct 26, 2016 at 6:16 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>> In a perfect world, it would be nice to add a new optional to "rbd
>>>>>>>>>>>> snap ls" to show all snapshots (with a new column to indicate the
>>>>>>>>>>>> associated namespace).
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Oct 25, 2016 at 11:07 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>> Question. When we print out snapshots of an image, should the group
>>>>>>>>>>>>> snapshots be listed, or should they be marked as special snapshots?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> V.
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 3:14 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>> Ok. I didn't have any intention to throw exceptions.
>>>>>>>>>>>>>> I was more concerned about whether it's ok to allocate and delete
>>>>>>>>>>>>>> objects or I should use smart pointers.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 7:18 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>> The only place exceptions are routinely used is within the "::decode"
>>>>>>>>>>>>>>> functions. I would prefer to see the code not throwing new exceptions
>>>>>>>>>>>>>>> on purpose.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Fri, Oct 7, 2016 at 2:26 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>> Are any exceptions used in librbd code? Should the code be exception safe?
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>>> V.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Fri, Sep 16, 2016 at 10:37 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>> On Thu, Sep 15, 2016 at 7:17 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>> if (struct_v >= 5) {
>>>>>>>>>>>>>>>>>> ::decode(snapshot_namespace, p);
>>>>>>>>>>>>>>>>>> } else {
>>>>>>>>>>>>>>>>>> snapshot_namespace = cls::rbd::UserSnapshotNamespace();
>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> then code for ::encode function of cls_rbd_snap would change accordingly:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> instead of
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> boost::apply_visitor(cls::rbd::EncodeSnapshotTypeVisitor(bl),
>>>>>>>>>>>>>>>>>> snapshot_namespace);
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> I would do:
>>>>>>>>>>>>>>>>>> ::encode(snapshot_namespace, bl);
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> +1 -- looks good to me
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> Jason
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Jason
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Jason
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Jason
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Jason
>>>
>>>
>>>
>>> --
>>> Jason
>
>
>
> --
> Jason
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