On 09/01/2016 11:52 AM, Dan Smith wrote:
The indirection service is really unrelated to this discussion, IMHO. If you take RPC out of the picture, all you have left is a direct-to-the-database facade to handle the fact that schema has expanded underneath you. As Clint (et al) have said -- designing the application to expect schema expansion (and avoiding unnecessary contraction) is the key here.
pretty much. there's no fixed pattern in how to do these. Every version of a data access API will be weighed down with baggage from the previous version and an inability to take full advantage of new improvements until the next release, and background migrations are complicated by the old application undoing their work. Even small migrations mean all these issues have to be considered each time on a case-by-case basis. These are the problems people are hoping to improve upon if possible. The spec at https://review.openstack.org/#/c/331740/ is discussing these issues in detail and is the first such specification I've seen that tries to get into it at this level.
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