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[Thierry Carrez <thierry.carrez+lp@xxxxxxxxx>]

** Changed in: nova
       Status: Fix Committed => Fix Released

** Changed in: nova
    Milestone: None => juno-rc1

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https://bugs.launchpad.net/bugs/1364986

Title:
  oslo.db now wraps all DB exceptions

Status in OpenStack Compute (Nova):
  Fix Released

Bug description:
  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

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