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

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

** Changed in: nova
    Milestone: None => havana-3

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https://bugs.launchpad.net/bugs/1204916

Title:
  Empty nova list causes expensive in predicate queries

Status in OpenStack Compute (Nova):
  Fix Released

Bug description:
  Requesting a list of servers through the API runs some queries that
  become more expensive when there are no instances returned.

  Example:

  /usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/expression.py:1927: SAWarning: The IN-predicate on "instance_system_metadata.instance_u
  uid" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate.  Consider alternati
  ve strategies for improved performance.
    return self._in_impl(operators.in_op, operators.notin_op, other)
  2013-07-24 20:42:46.126 DEBUG sqlalchemy.pool.QueuePool [-] Connection <_mysql.connection open to 'localhost' at 60bc290> checked out from po
  ol from (pid=24610) __init__ /usr/local/lib/python2.7/dist-packages/sqlalchemy/pool.py:415
  2013-07-24 20:42:46.127 INFO sqlalchemy.engine.base.Engine [-] SELECT instance_system_metadata.created_at AS instance_system_metadata_created_at, instance_system_metadata.updated_at AS instance_system_metadata_updated_at, instance_system_metadata.deleted_at AS instance_system_metadata_deleted_at, instance_system_metadata.deleted AS instance_system_metadata_deleted, instance_system_metadata.id AS instance_system_metadata_id, instance_system_metadata.`key` AS instance_system_metadata_key, instance_system_metadata.value AS instance_system_metadata_value, instance_system_metadata.instance_uuid AS instance_system_metadata_instance_uuid 
  FROM instance_system_metadata 
  WHERE instance_system_metadata.deleted = %s AND instance_system_metadata.instance_uuid != instance_system_metadata.instance_uuid

  instance_system_metadata, instance_metadata, and instance_faults all
  do the same thing.  You can see by the WHERE clause that this will not
  return any rows, but it still scans a large part of the tables.

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