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Speaking as a ‘database guy’ and a ‘Trove guy’, I’ll say this; “Metadata” is a very generic term and the meaning of “metadata” in a database context is very different from the meaning of “metadata” in the context that Glance is providing. 

 

Furthermore the usage and access pattern for this metadata, the frequency of change, and above all the frequency of access are fundamentally different between Trove and what Glance appears to be offering, and we should probably not get too caught up in the project “title”.

 

We would not be “reinventing the wheel” if we implemented an independent metadata scheme for Trove; we would be implementing the right kind of when for the vehicle that we are operating. Therefore I do not agree with your characterization that concludes that:

 

>> given goals at [1] are out of scope of Database program, etc

 

Just to be clear, when you write:

 

>> Unfortunately, we’re(Trove devs) are on half way to metadata …

 

it is vital to understand that our view of “metadata” is very different from (for example, a file system’s view of metadata, or potentially Glance’s view of metadata). For that reason, I believe that your comments on https://review.openstack.org/#/c/82123/16 are also somewhat extreme.

 

Before postulating a solution (or “delegating development to Glance devs”), it would be more useful to fully describe the problem being solved by Glance and the problem(s) we are looking to solve in Trove, and then we could have a meaningful discussion about the right solution. 

 

I submit to you that we will come away concluding that there is a round peg, and a square hole. Yes, one will fit in the other but the final product will leave neither party particularly happy with the end result.

 

-amrith

 

From: Denis Makogon [mailto:dmakogon at mirantis.com] 
Sent: Thursday, July 24, 2014 9:33 AM
To: OpenStack Development Mailing List
Subject: [openstack-dev] [Glance][Trove] Metadata Catalog

 

Hello, Stackers.


     I’d like to discuss the future of Trove metadata API. But first small history info (mostly taken for Trove medata spec, see [1]):

Instance metadata is a feature that has been requested frequently by our users. They need a way to store critical information for their instances and have that be associated with the instance so that it is displayed whenever that instance is listed via the API. This also becomes very usable from a testing perspective when doing integration/ci. We can utilize the metadata to store things like what process created the instance, what the instance is being used for, etc... The design for this feature is modeled heavily on the Nova metadata API with a few tweaks in how it works internally.

    And here comes conflict. Glance devs are working on “Glance Metadata Catalog” feature (see [2]). And as for me, we don’t have to “reinvent the wheel” for Trove. It seems that we would be able 

to use Glance API to interact with   Metadata Catalog. And it seems to be redundant to write our own API for metadata CRUD operations.

    

    From Trove perspective, we need to define a list concrete use cases for metadata usage (eg given goals at [1] are out of scope of Database program, etc.). 

>From development and cross-project integration perspective, we need to delegate all development to Glance devs. But we still able to help Glance devs with this feature by taking active part in polishing proposed spec (see [2]).

    

    Unfortunately, we’re(Trove devs) are on half way to metadata - patch for python-troveclient already merged. So, we need to consider deprecation/reverting of merged and block 

merging of proposed ( see [3]) patchsets in favor of Glance Metadata Catalog.



    Thoughts?

[1]  <https://wiki.openstack.org/wiki/Trove-Instance-Metadata> https://wiki.openstack.org/wiki/Trove-Instance-Metadata

[2]  <https://review.openstack.org/#/c/98554/11> https://review.openstack.org/#/c/98554/11

[3]  <https://review.openstack.org/#/c/82123/> https://review.openstack.org/#/c/82123/

 

Best regards,

Denis Makogon

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