oslo.db now wraps all DB exceptions

[Roman Podoliaka]

tl;dr

In a few versions of oslo.db (maybe when we release 1.0.0?), every project using oslo.db should inspect their code and remove usages of 'raw' DB exceptions like IntegrityError/OperationalError/etc from except clauses and replace them with the corresponding custom exceptions from oslo.db (at least a base one - DBError).

Full version

A recent commit to oslo.db changed the way the 'raw' DB exceptions are wrapped (e.g. IntegrityError, OperationalError, etc). Previously, we used decorators on Session methods and wrapped those exceptions with oslo.db custom ones. This is mostly useful for handling them later (e.g. to retry DB API methods on deadlocks).

The problem with Session decorators was that it wasn't possible to catch and wrap all possible exceptions. E.g. SA Core exceptions and exceptions raised in Query.all() calls were ignored. Now we are using a low level SQLAlchemy event to catch all possible DB exceptions. This means that if consuming projects had workarounds for those cases and expected 'raw' exceptions instead of oslo.db ones, they would be broken. That's why we *temporarily* added both 'raw' exceptions and new ones to expect clauses in consuming projects code when they were ported to using of oslo.db to make the transition smooth and allow them to work with different oslo.db versions.

On the positive side, we now have a solution for problems like https://bugs.launchpad.net/nova/+bug/1283987 when exceptions in Query methods calls weren't handled properly.

In a few releases of oslo.db we can safely remove 'raw' DB exceptions like IntegrityError/OperationalError/etc from projects code and except only oslo.db specific ones like DBDuplicateError/DBReferenceError/DBDeadLockError/etc (at least, we wrap all the DB exceptions with our base exception DBError, if we haven't found a better match).

oslo.db exceptions and their description: https://github.com/openstack/oslo.db/blob/master/oslo/db/exception.py

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/101901
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=1b83b2f11054ddd3f72fe75c5cef496060afcb3a
Submitter: Jenkins
Branch: master

commit 1b83b2f11054ddd3f72fe75c5cef496060afcb3a
Author: Andrey Kurilin <email address hidden>
Date: Sat Jun 21 13:56:42 2014 +0300

    Move to oslo.db

    Replace common oslo code nova.openstack.common.db by usage
    of oslo.db library and remove common code.

    Replaced catching of raw sqlalchemy exceptions by catches
    of oslo.db exceptions(such as DBError, DBDuplicateEntry, etc).

    Co-Authored-By: Eugeniya Kudryashova <email address hidden>

    Closes-Bug: #1364986
    Closes-Bug: #1353131
    Closes-Bug: #1283987
    Closes-Bug: #1274523
    Change-Id: I0649539e071b2318ec85ed5d70259c949408e64b