[Bug 1552971] Re: InstanceList.get_by_security_group_id can run very slow

[Edward Hope-Morley]

** Also affects: cloud-archive
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1552971

Title:
  InstanceList.get_by_security_group_id can run very slow

Status in Ubuntu Cloud Archive:
  New
Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) mitaka series:
  Fix Committed

Bug description:
  The nova.objects.instance.InstanceList class's
  get_by_security_group_id function calls the db.security_group_get
  function, which uses the _security_group_get_query() function to
  generate a query object. That query, by default, joins with the
  secgroup-rules table, and currently the db.security_group_get function
  offers no option to avoid joining with the rules. As a result:

  If a group-source secgroup-rule exists on a security group with a
  large number of instances and a large number of rules, the db query
  result will be very large and take multiple seconds to complete, tying
  up conductor and making the system unresponsive.

  Since the InstanceList.get_by_security_group_id call only aims to
  build a list of instances, there is no need in this case to join with
  the rules, and so the db.security_group_get call should optionally
  avoid joining with the rules table.

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