in-progress queries are intolerant of mysql restarts

[Therese McHale]

Glance is intolerant of mysql restarts with running queries and the currently ping_listener/wrap_db_error mechanism does not work for running queries. This was logged in Bug #954971 and a solution (using wrap_db for queries) merged. The fix was removed in Bug #967887 as it did not work with later versions of sqlalchemy.
An alternative approach is to use the sqlalchemy create_engine "module" parameter to override the engine behaviour and do the wrapping there. (Mike Bayer of sqlalchemys recommended solution) I will attach a patch which does this

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/11874

[Brian Waldon (bcwaldon)]

Let's look at this in Grizzly

[Viktor Serhieiev (vsergeyev)]

Well, oslo.db supports retrying of transactions. Folks, from Glance/Nova - can you please check it?

[Viktor Serhieiev (vsergeyev)]

Mark as Incomplete in oslo.db because of low information about a bug

[Mike Bayer (zzzeek)]

I think part of the topic here is that there are two ways I've proposed of retrying transactions. The simple, easy and boring one we have is the wrap_db_retry() decorator. The other one is an exotic event-based approach I did for a client, which I feel is pretty experimental which is over at https://bitbucket.org/zzzeek/sqlalchemy/issue/3104/transaction-replay-extension , the attached patch is already in production elsewhere. The experimental design actually records all the SQL as the transaction proceeds, intercepts a selected set of exceptions as "good for retry" and then replays a subset of that SQL back, namely the DML. This is a very exotic way to go as it makes a lot of assumptions that those same INSERT/UPDATE/DELETE statements are still valid, even though we're in a new transaction.

I have a notion that we should ultimately have all methods that start using a database transaction wrapped in a decorator that establishes this context. The retry of the whole method should probably be rolled into that decorator.

[Sean Dague (sdague)]

I'm not clear where this bug still stands. Marking as incomplete for Nova.

[Markus Zoeller (markus_z) (mzoeller)]

This bug has the status "incomplete" for more than 30 days. It is unclear if this is an "invalid" bug or if it is an "opinion". I set it to "won't fix".
Feel free to reopen the bug by providing the requested information and set the bug status back to "New".

[Roman Podoliaka (rpodolyaka)]

On oslo.db side we can track this as a feature request for EngineFacade to be able to retry transactions automatically.