diff --git a/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/031_request_specs_spec_mediumtext.py b/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/031_request_specs_spec_mediumtext.py
new file mode 100644
index 000000000000..e0eef79a022c
--- /dev/null
+++ b/nova/db/sqlalchemy/api_migrations/migrate_repo/versions/031_request_specs_spec_mediumtext.py
@@ -0,0 +1,25 @@
+#    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.
+
+from sqlalchemy import MetaData
+from sqlalchemy import Table
+
+from nova.db.sqlalchemy import api_models
+
+
+def upgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    request_specs = Table('request_specs', meta, autoload=True)
+    if request_specs.c.spec.type != api_models.MediumText():
+        request_specs.c.spec.alter(type=api_models.MediumText())
diff --git a/nova/db/sqlalchemy/api_models.py b/nova/db/sqlalchemy/api_models.py
index e5c5720dc3b0..586b8b3feab5 100644
--- a/nova/db/sqlalchemy/api_models.py
+++ b/nova/db/sqlalchemy/api_models.py
@@ -168,7 +168,7 @@ class RequestSpec(API_BASE):
 
     id = Column(Integer, primary_key=True)
     instance_uuid = Column(String(36), nullable=False)
-    spec = Column(Text, nullable=False)
+    spec = Column(MediumText(), nullable=False)
 
 
 class Flavors(API_BASE):
diff --git a/nova/tests/functional/db/api/test_migrations.py b/nova/tests/functional/db/api/test_migrations.py
index b66e2623dcac..d0e8c3c4ec8e 100644
--- a/nova/tests/functional/db/api/test_migrations.py
+++ b/nova/tests/functional/db/api/test_migrations.py
@@ -35,6 +35,7 @@ import mock
 from oslo_db.sqlalchemy import test_base
 from oslo_db.sqlalchemy import test_migrations
 from oslo_db.sqlalchemy import utils as db_utils
+from oslo_serialization import jsonutils
 import sqlalchemy
 from sqlalchemy.engine import reflection
 
@@ -43,6 +44,7 @@ from nova.db.sqlalchemy.api_migrations import migrate_repo
 from nova.db.sqlalchemy import api_models
 from nova.db.sqlalchemy import migration as sa_migration
 from nova import test
+from nova.test import uuids
 from nova.tests import fixtures as nova_fixtures
 
 
@@ -578,6 +580,34 @@ class NovaAPIMigrationsWalk(test_migrations.WalkVersionsMixin):
         for column in ['created_at', 'updated_at', 'id', 'uuid']:
             self.assertColumnExists(engine, 'placement_aggregates', column)
 
+    def _pre_upgrade_031(self, engine):
+        request_specs = db_utils.get_table(engine, 'request_specs')
+        # The spec value is a serialized json blob.
+        spec = jsonutils.dumps(
+            {"instance_group": {"id": 42,
+                                "members": ["uuid1",
+                                            "uuid2",
+                                            "uuid3"]}})
+        fake_request_spec = {
+            'id': 42, 'spec': spec, 'instance_uuid': uuids.instance}
+        request_specs.insert().execute(fake_request_spec)
+
+    def _check_031(self, engine, data):
+        request_specs = db_utils.get_table(engine, 'request_specs')
+        if engine.name == 'mysql':
+            self.assertIsInstance(request_specs.c.spec.type,
+                                  sqlalchemy.dialects.mysql.MEDIUMTEXT)
+
+        expected_spec = {"instance_group": {"id": 42,
+                                            "members": ["uuid1",
+                                                        "uuid2",
+                                                        "uuid3"]}}
+        from_db_request_spec = request_specs.select(
+            request_specs.c.id == 42).execute().first()
+        self.assertEqual(uuids.instance, from_db_request_spec['instance_uuid'])
+        db_spec = jsonutils.loads(from_db_request_spec['spec'])
+        self.assertDictEqual(expected_spec, db_spec)
+
 
 class TestNovaAPIMigrationsWalkSQLite(NovaAPIMigrationsWalk,
                                       test_base.DbTestCase,
diff --git a/releasenotes/notes/bug-1738094-request_specs.spec-migration-22d3421ea1536a37.yaml b/releasenotes/notes/bug-1738094-request_specs.spec-migration-22d3421ea1536a37.yaml
new file mode 100644
index 000000000000..c333cc93e748
--- /dev/null
+++ b/releasenotes/notes/bug-1738094-request_specs.spec-migration-22d3421ea1536a37.yaml
@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    This release contains a schema migration for the ``nova_api`` database
+    in order to address bug 1738094:
+
+    https://bugs.launchpad.net/nova/+bug/1738094
+
+    The migration is optional and can be postponed if you have not been
+    affected by the bug. The bug manifests itself through "Data too long for
+    column 'spec'" database errors.