Add share instance index on share_id

The index on the foreign key is created on InnoDB mysql implicitly.
This makes it explicit.

Closes-Bug: #1776495
Change-Id: I6ff5cee86997d0d756b4852fa4d0e7bcfcc9c1cf

manila/db/migrations/alembic/versions/097fad24d2fc_add_share_instances_share_id_index.py

@@ -0,0 +1,42 @@
+# Copyright 2018 SAP SE
+#
+#    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_share_instances_share_id_index
+
+Revision ID: 097fad24d2fc
+Revises: 0274d20c560f
+Create Date: 2018-06-12 10:06:50.642418
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '097fad24d2fc'
+down_revision = '0274d20c560f'
+
+from alembic import op
+
+
+INDEX_NAME = 'share_instances_share_id_idx'
+TABLE_NAME = 'share_instances'
+
+
+def upgrade():
+    op.create_index(INDEX_NAME, TABLE_NAME, ['share_id'])
+
+
+def downgrade():
+    op.drop_constraint('si_share_fk', TABLE_NAME, type_='foreignkey')
+    op.drop_index(INDEX_NAME, TABLE_NAME)
+    op.create_foreign_key(
+        'si_share_fk', TABLE_NAME, 'shares', ['share_id'], ['id'])

manila/tests/db/migrations/alembic/migrations_data_checks.py

@@ -2666,3 +2666,24 @@ class ShareInstanceAccessMapTableChecks(BaseMigrationChecks):
             elif share_access['id'] == self.error_share_access['id']:
                 self.test_case.assertEqual(
                     constants.ACCESS_STATE_ERROR, share_access['state'])
+
+
+@map_to_migration('097fad24d2fc')
+class ShareInstancesShareIdIndexChecks(BaseMigrationChecks):
+
+    def setup_upgrade_data(self, engine):
+        pass
+
+    def _get_share_instances_share_id_index(self, engine):
+        share_instances_table = utils.load_table('share_instances', engine)
+        for idx in share_instances_table.indexes:
+            if idx.name == 'share_instances_share_id_idx':
+                return idx
+
+    def check_upgrade(self, engine, data):
+        self.test_case.assertTrue(
+            self._get_share_instances_share_id_index(engine))
+
+    def check_downgrade(self, engine):
+        self.test_case.assertFalse(
+            self._get_share_instances_share_id_index(engine))