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[Mohammed Naser <1878979@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

The function which counts resources using the legacy method involves
getting a list of all cell mappings assigned to a specific project:

https://github.com/openstack/nova/blob/575a91ff5be79ac35aef4b61d84c78c693693304/nova/quota.py#L1170-L1209

This code can be very heavy on a database which contains a lot of
instances (but not a lot of mappings), potentially scanning millions of
rows to gather 1-2 cell mappings.  In a single cell environment, it is
just extra CPU usage with exactly the same outcome.

The [api]/instance_list_per_project_cells was introduced to workaround
this:

https://github.com/openstack/nova/blob/575a91ff5be79ac35aef4b61d84c78c693693304/nova/compute/instance_list.py#L146-L153

However, the quota code does not implement it which means quota count
take a big toll on the database server.  We should ideally mirror the
same behaviour in the quota code.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1878979

Title:
  Quota code does not respect [api]/instance_list_per_project_cells

Status in OpenStack Compute (nova):
  New

Bug description:
  The function which counts resources using the legacy method involves
  getting a list of all cell mappings assigned to a specific project:

  https://github.com/openstack/nova/blob/575a91ff5be79ac35aef4b61d84c78c693693304/nova/quota.py#L1170-L1209

  This code can be very heavy on a database which contains a lot of
  instances (but not a lot of mappings), potentially scanning millions
  of rows to gather 1-2 cell mappings.  In a single cell environment, it
  is just extra CPU usage with exactly the same outcome.

  The [api]/instance_list_per_project_cells was introduced to workaround
  this:

  https://github.com/openstack/nova/blob/575a91ff5be79ac35aef4b61d84c78c693693304/nova/compute/instance_list.py#L146-L153

  However, the quota code does not implement it which means quota count
  take a big toll on the database server.  We should ideally mirror the
  same behaviour in the quota code.

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