1 files changed, 17 insertions, 2 deletions
diff --git a/synapse/storage/schema/__init__.py b/synapse/storage/schema/__init__.py
index f0d9f23167..d36ba1d773 100644
--- a/synapse/storage/schema/__init__.py
+++ b/synapse/storage/schema/__init__.py
@@ -12,6 +12,21 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Remember to update this number every time a change is made to database
-# schema files, so the users will be informed on server restarts.
 SCHEMA_VERSION = 59
+"""Represents the expectations made by the codebase about the database schema
+
+This should be incremented whenever the codebase changes its requirements on the
+shape of the database schema (even if those requirements are backwards-compatible with
+older versions of Synapse).
+
+See `README.md <synapse/storage/schema/README.md>`_  for more information on how this
+works.
+"""
+
+
+SCHEMA_COMPAT_VERSION = 59
+"""Limit on how far the synapse codebase can be rolled back without breaking db compat
+
+This value is stored in the database, and checked on startup. If the value in the
+database is greater than SCHEMA_VERSION, then Synapse will refuse to start.
+"""