Fix inconsistent ordering caused by low datetime precision.

The low datetime precision of created_at, updated_at,
deleted_at fields on MySQL can lead to inconsistent list
of returned items when used with --limit.

Change-Id: I6e4b3a38defc1d916556c7cdddfaaab854432ea1
Closes-Bug: #1859474

manila/db/migrations/alembic/versions/fbdfabcba377_change_the_mysql_datetime_precision.py

@@ -0,0 +1,78 @@
+# 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.
+
+"""Change the datetime precision for all objects (MySQL and derivatives)
+
+Revision ID: fbdfabcba377
+Revises: 478c445d8d3e
+Create Date: 2020-04-20 15:32:59.365323
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'fbdfabcba377'
+down_revision = '478c445d8d3e'
+
+from alembic import op
+from sqlalchemy import DateTime, dialects
+
+
+# DB Tables that can be affected by low precision timestamps in MySQL:
+TABLES = ('services', 'quotas', 'project_user_quotas', 'backend_info',
+          'project_share_type_quotas', 'quota_classes', 'quota_usages',
+          'reservations', 'shares', 'share_instance_export_locations',
+          'share_instances', 'share_instance_export_locations_metadata',
+          'share_types', 'share_type_projects', 'share_type_extra_specs',
+          'share_metadata', 'share_access_map', 'share_access_rules_metadata',
+          'share_instance_access_map', 'share_snapshot_instances',
+          'share_snapshots', 'share_snapshot_access_map', 'share_networks',
+          'share_snapshot_instance_access_map', 'share_network_subnets',
+          'share_snapshot_instance_export_locations', 'security_services',
+          'share_servers', 'share_server_backend_details', 'share_groups',
+          'network_allocations', 'share_network_security_service_association',
+          'drivers_private_data', 'availability_zones', 'share_group_types',
+          'share_group_type_projects', 'share_group_type_specs', 'messages',
+          'share_group_snapshots', 'share_group_type_share_type_mappings',
+          'share_group_share_type_mappings')
+
+
+def upgrade():
+    context = op.get_context()
+
+    if context.bind.dialect.name == 'mysql':
+        # override the default precision of DateTime:
+        for table in TABLES:
+            op.alter_column(table, 'created_at',
+                            existing_type=DateTime,
+                            type_=dialects.mysql.DATETIME(fsp=6))
+            op.alter_column(table, 'updated_at',
+                            existing_type=DateTime,
+                            type_=dialects.mysql.DATETIME(fsp=6))
+            op.alter_column(table, 'deleted_at',
+                            existing_type=DateTime,
+                            type_=dialects.mysql.DATETIME(fsp=6))
+
+
+def downgrade():
+    context = op.get_context()
+
+    if context.bind.dialect.name == 'mysql':
+        for table in TABLES:
+            op.alter_column(table, 'created_at',
+                            existing_type=dialects.mysql.DATETIME(fsp=6),
+                            type_=DateTime)
+            op.alter_column(table, 'updated_at',
+                            existing_type=dialects.mysql.DATETIME(fsp=6),
+                            type_=DateTime)
+            op.alter_column(table, 'deleted_at',
+                            existing_type=dialects.mysql.DATETIME(fsp=6),
+                            type_=DateTime)