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Reviewed:  https://review.openstack.org/281116
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=e174e619580173d43b398aa71587938a4313ca5b
Submitter: Jenkins
Branch:    master

commit e174e619580173d43b398aa71587938a4313ca5b
Author: venkata anil <anilvenkata@xxxxxxxxxx>
Date:   Wed Apr 13 13:50:05 2016 +0000

    Avoid calling _get_subnet(s) multiple times in ipam driver
    
    While allocating or updating ips for port, _get_subnet and
    _get_subnets were called multiple times resulting in multiple DB
    calls.  This patch changes it to only call _get_subnets once
    initially.
    
    Closes-bug: #1554414
    Change-Id: I7124974bac629fdb8946df6a7f84bd6b40f5af49


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

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https://bugs.launchpad.net/bugs/1554414

Title:
  Avoid calling _get_subnet(s) multiple times in ipam driver

Status in neutron:
  Fix Released

Bug description:
  While allocating or updating ips for port, _get_subnet and _get_subents are called multiple times.
  (note: Fix for this bug is needed for PD change https://review.openstack.org/#/c/241227 )

  For example, if update_port is called with below fixed_ips
  fixed_ips = [{'subnet_id': 'subnet1'},
               {'subnet_id': 'v6_dhcp_stateless_subnet'}
               {'subnet_id': 'v6_slaac_subnet'}
               {'subnet_id': 'v6_pd_subnet'}
               {'subnet_id': 'subnet4', 'ip_address': '30.0.0.3'}
               {'ip_address': '40.0.0.4'}
               {'ip_address': '50.0.0.5'}}
  then through _test_fixed_ips_for_port(fixed_ips),  "_get_subnet"[1] is called 4 times for subnet1, v6_dhcp_stateless_subnet, v6_slaac_subnet, v6_pd_subnet, subnet4. "_get_subnets" [2] is called 2 times for ip_address 40.0.0.4 and 50.0.0.5.

  If in case of _test_fixed_ips_for_port called for
  _allocate_ips_for_port, then _get_subnets is already called at[3] (so
  increase call count). So incase of _allocate_ips_for_port, if we save
  subnets from [3] saved in local variable and use that in-memory
  subnets in further calls, we can avoid above calls to DB.

  Sometimes when subnet is updated, update_subnet may trigger
  update_port(fixed_ips)[4] for all ports on the subnet. And in each
  port's fixed_ips, if we have multiple subnets and ip_addresses then
  _get_subnet and _get_subnets will be called for multiple times for
  each port like above example. For example in above case if we have 10
  ports on the subnet, then update_subnet will result in (10*6=60) 60
  times DB access instead of 10 DB access.

  When port_update is called for PD subnet, it again calls get_subnet
  for each fixed_ip[5], to check if subnet is PD subnet or not(after
  get_subnet and get_subnets called many times in
  _test_fixed_ips_for_port).

  In all above cases, for _get_subnet and _get_subnets, we are accessing DB many times.
   So instead of calling get_subnet or get_subnets for each fixed_ip of a port(at multiple places), we can call get_subnets of a network at begining of _allocate_ips_for_port(for create port) and _update_ips_for_port(during update) and use the in-memory subnets in subsequent private functions.

  [1] https://github.com/openstack/neutron/blob/master/neutron/db/ipam_backend_mixin.py#L311
  [2] https://github.com/openstack/neutron/blob/master/neutron/db/ipam_backend_mixin.py#L331
  [3] https://github.com/openstack/neutron/blob/master/neutron/db/ipam_pluggable_backend.py#L192
  [4] https://github.com/openstack/neutron/blob/master/neutron/db/db_base_plugin_v2.py#L785
  [5] https://review.openstack.org/#/c/241227/11/neutron/db/ipam_non_pluggable_backend.py Lines 284 and 334.

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