Add device_id index to Port

Some 'Port' queries use 'device_id' column for lookup.
Such queries could be observed in database query log (at least) during
instance launch. In the absence of 'device_id' index that leads to full
table scan. That causes unnecessary database load and impacts query
response time.

Change-Id: If42b7d3265e216d393d3ab8c172b97637af908cc
Closes-Bug: #1574750

neutron/db/migration/alembic_migrations/versions/EXPAND_HEAD

@@ -1 +1 @@
-5abc0278ca73
+d3435b514502

neutron/db/migration/alembic_migrations/versions/newton/expand/d3435b514502_add_device_id_index_to_port.py

@@ -0,0 +1,32 @@
+# Copyright 2016 OpenStack Foundation
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+#
+
+"""Add device_id index to Port
+
+Revision ID: d3435b514502
+Revises: 5abc0278ca73
+Create Date: 2016-04-25 22:13:16.676761
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'd3435b514502'
+down_revision = '5abc0278ca73'
+
+from alembic import op
+
+
+def upgrade():
+    op.create_index('ix_ports_device_id', 'ports', ['device_id'], unique=False)

neutron/db/models_v2.py

@@ -135,6 +135,7 @@ class Port(model_base.HasStandardAttributes, model_base.BASEV2,
             'ix_ports_network_id_mac_address', 'network_id', 'mac_address'),
         sa.Index(
             'ix_ports_network_id_device_owner', 'network_id', 'device_owner'),
+        sa.Index('ix_ports_device_id', 'device_id'),
         sa.UniqueConstraint(
             network_id, mac_address,
             name='uniq_ports0network_id0mac_address'),