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[Attila Fazekas <afazekas@xxxxxxxxxx>]

Public bug reported:

/usr/lib64/python2.7/site-
packages/sqlalchemy/sql/default_comparator.py:35: SAWarning: The IN-
predicate on "instances.uuid" was invoked with an empty sequence. This
results in a contradiction, which nonetheless can be expensive to
evaluate.  Consider alternative strategies for improved performance.

The above warning reported in the n-cond (or n-cpu) log when using
SQLAlchemy 0.9.8.

The system doing an invain query at the end.

The warning generated by this code part:
https://github.com/openstack/nova/blob/9fd059b938a2acca8bf5d58989c78d834fbb0ad8/nova/compute/manager.py#L696
driver_uuids can be an empty list. In this case the sql query is not necessary.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1383617

Title:
  SAWarning contradiction IN-predicate on "instances.uuid"

Status in OpenStack Compute (Nova):
  New

Bug description:
  /usr/lib64/python2.7/site-
  packages/sqlalchemy/sql/default_comparator.py:35: SAWarning: The IN-
  predicate on "instances.uuid" was invoked with an empty sequence. This
  results in a contradiction, which nonetheless can be expensive to
  evaluate.  Consider alternative strategies for improved performance.

  The above warning reported in the n-cond (or n-cpu) log when using
  SQLAlchemy 0.9.8.

  The system doing an invain query at the end.

  The warning generated by this code part:
  https://github.com/openstack/nova/blob/9fd059b938a2acca8bf5d58989c78d834fbb0ad8/nova/compute/manager.py#L696
  driver_uuids can be an empty list. In this case the sql query is not necessary.

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