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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">There’s also some similar situations when we actually don’t lock on resources. For example – a cgsnapshot may get deleted while creating a consistencygroup from
it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">From my perspective it seems best to have atomic state changes and state-based exclusion in API. We would need some kind of currently_used_to_create_snapshot/volums/consistencygroups
states to achieve that. Then we would be also able to return VolumeIsBusy exceptions so retrying a request would be on the user side.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Duncan Thomas [mailto:duncan.thomas@gmail.com]
<br>
<b>Sent:</b> Sunday, June 28, 2015 12:16 PM<br>
<b>To:</b> OpenStack Development Mailing List<br>
<b>Subject:</b> Re: [openstack-dev] [cinder][oslo] Locks for create from volume/snapshot<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>We need mutual exclusion for several operations. Whether that is done by entity queues, locks, state based locking at the api later, or something else, we need mutual exclusion.<o:p></o:p></p>
<p>Our current api does not lend itself to looser consistency, and I struggle to come up with a sane api that does - nobody doing an operation on a volume wants it to happen maybe, at some time...<o:p></o:p></p>
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<p class="MsoNormal">On 28 Jun 2015 07:30, "Avishay Traeger" <<a href="mailto:avishay@stratoscale.com">avishay@stratoscale.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Do we really need any of these locks? I'm sure we could come up with some way to remove them, rather than make them distributed.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Sun, Jun 28, 2015 at 5:07 AM, Joshua Harlow <<a href="mailto:harlowja@outlook.com" target="_blank">harlowja@outlook.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">John Griffith wrote:<o:p></o:p></p>
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<br>
On Sat, Jun 27, 2015 at 11:47 AM, Joshua Harlow <<a href="mailto:harlowja@outlook.com" target="_blank">harlowja@outlook.com</a><o:p></o:p></p>
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<p class="MsoNormal"><mailto:<a href="mailto:harlowja@outlook.com" target="_blank">harlowja@outlook.com</a>>> wrote:<br>
<br>
Duncan Thomas wrote:<br>
<br>
We are working on some sort of distributed replacement for the<br>
locks in<br>
cinder, since file locks are limiting our ability to do HA. I'm<br>
afraid<br>
you're unlikely to get any traction until that work is done.<br>
<br>
I also have a concern that some backend do not handle load well,<br>
and so<br>
benefit from the current serialisation. It might be necessary to<br>
push<br>
this lock down into the driver and allow each driver to choose it's<br>
locking model for snapshots.<br>
<br>
<br>
IMHO (and I know this isn't what everyone thinks) but I'd rather<br>
have cinder (and other projects) be like this from top gear (<br>
<a href="https://www.youtube.com/watch?v=xnWKz7Cthkk" target="_blank">https://www.youtube.com/watch?v=xnWKz7Cthkk</a> ) where that toyota<br>
truck is virtually indestructible vs. trying to be a<br>
high-maintenance ferrari (when most openstack projects do a bad job<br>
of trying to be one). So, maybe for a time (and I may regret saying<br>
this) we could consider focusing on reliability, consistency, being<br>
the toyota vs. handling some arbitrary amount of load (trying to be<br>
a ferrari).<br>
<br>
Also I'd expect/think operators would rather prefer a toyota at this<br>
stage of openstack :) Ok enough analogies, ha.<br>
<br>
<br>
Well said Josh, I guess I've been going about this all wrong by not<br>
using the analogies :)<o:p></o:p></p>
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Exactly!! IMHO should be the new 'openstack mantra, built from components/projects that survive like a toyota truck' haha. Part 2 (<a href="https://www.youtube.com/watch?v=xTPnIpjodA8" target="_blank">https://www.youtube.com/watch?v=xTPnIpjodA8</a>) and part
3 (<a href="https://www.youtube.com/watch?v=kFnVZXQD5_k" target="_blank">https://www.youtube.com/watch?v=kFnVZXQD5_k</a>) are funny/interesting also :-P<br>
<br>
Now we just need openstack to be that reliable and tolerant of failures/calamities/...<o:p></o:p></p>
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<br>
-Josh<br>
<br>
<br>
On 27 Jun 2015 06:18, "niuzhenguo" <<a href="mailto:niuzhenguo@huawei.com" target="_blank">niuzhenguo@huawei.com</a><br>
<mailto:<a href="mailto:niuzhenguo@huawei.com" target="_blank">niuzhenguo@huawei.com</a>><br>
<mailto:<a href="mailto:niuzhenguo@huawei.com" target="_blank">niuzhenguo@huawei.com</a> <mailto:<a href="mailto:niuzhenguo@huawei.com" target="_blank">niuzhenguo@huawei.com</a>>>><o:p></o:p></p>
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<p class="MsoNormal"><br>
wrote:<br>
<br>
Hi folks,____<br>
<br>
__ __<br>
<br>
Currently we use a lockfile to protect the create<br>
operations from<br>
concurrent delete the source volume/snapshot, we use<br>
exclusive____<br>
<br>
locks on both delete and create sides which will ensure<br>
that:____<br>
<br>
__ __<br>
<br>
__1.__If a create of VolA from snap/VolB is in progress,<br>
any delete<br>
requests for snap/VolB will wait until the create is<br>
complete.____<br>
<br>
__2.__If a delete of snap/VolA is in progress, any create from<br>
snap/VolA will wait until snap/VolA delete is complte.____<br>
<br>
__ __<br>
<br>
but, the exclusive locks will also result in:____<br>
<br>
__ __<br>
<br>
__3.__If a create of VolA from snap/VolB is inprogress, any<br>
other<br>
create requests from snap/VolB will wait until the create is<br>
complete. ____<br>
<br>
__ __<br>
<br>
So the create operations from same volume/snapshot can not<br>
process<br>
on parallel, please reference bp [1].____<br>
<br>
I’d like to change the current filelock or introduce a new<br>
lock to<br>
oslo.concurrency.____<br>
<br>
__ __<br>
<br>
Proposed change:____<br>
<br>
Add exclusive(write) locks for delete operations and<br>
shared(read)<br>
locks for create operations, to ensure that create from<br>
volume/snapshot____<br>
<br>
can work on parallel and protect create operations from<br>
concurrent<br>
delete the source volume/snapshot.____<br>
<br>
__ __<br>
<br>
I’d like to get what’s your suggestions, thanks in advance.____<br>
<br>
__ __<br>
<br>
[1]<br>
<a href="https://blueprints.launchpad.net/cinder/+spec/enhance-locks____" target="_blank">
https://blueprints.launchpad.net/cinder/+spec/enhance-locks____</a><br>
<br>
__ __<br>
<br>
__ __<br>
<br>
-zhenguo____<br>
<br>
<br>
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<p class="MsoNormal"><span style="color:#666666">E-mail: <a href="mailto:avishay@stratoscale.com" target="_blank"><span style="color:#1155CC">avishay@stratoscale.com</span></a></span><o:p></o:p></p>
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