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[OpenStack Infra <1760322@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/558068
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e2924ba2379adc19e7ebd07ead8efd5e9c8e367d
Submitter: Zuul
Branch:    master

commit e2924ba2379adc19e7ebd07ead8efd5e9c8e367d
Author: Eric Fried <efried@xxxxxxxxxx>
Date:   Sat Mar 31 11:42:52 2018 -0500

    Use an independent transaction for _trait_sync
    
    Provides a fix for the referenced bug by using an independent
    transaction for the _trait_sync method, meaning it gets committed right
    away regardless of what happens in the calling scope.
    
    Change-Id: Ie9731d0df8cf52acdc7a442316a35798a4fed4cb
    Closes-Bug: 1760322


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1760322

Title:
  Traits not synced if first retrieval fails

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  If the first trait you try to retrieve from placement doesn't exist,
  traits are not synced from os_traits into the database, so it winds up
  empty.

          try:
              rp_obj.Trait.get_by_name(self.ctx, 'CUSTOM_GOLD')
          except exception.TraitNotFound:
              pass
          rp_obj.Trait.get_by_name(self.ctx, os_traits.HW_CPU_X86_AVX2)  # <== raises TraitNotFound

  I *think* what's happening is this:

  1    @staticmethod
  2    @db_api.api_context_manager.writer  # trait sync can cause a write
  3    def _get_by_name_from_db(context, name):
  4        _ensure_trait_sync(context)
  5        result = context.session.query(models.Trait).filter_by(
  6            name=name).first()
  7        if not result:
  8            raise exception.TraitNotFound(names=name)
  9        return result

  Line 4 "succeeds" and sets _TRAITS_SYNCED = True.
  But because line 8 raises, the transaction is rolled back.  Database stays empty.
  Subsequent retrieval attempts see _TRAITS_SYNCED == True so don't try to resync.

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