Bail during start-up if there are old background updates.

2 files changed, 42 insertions, 1 deletions

diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 31501fd573..9275253277 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -32,7 +32,11 @@ import attr
 from synapse.config.homeserver import HomeServerConfig
 from synapse.storage.database import LoggingDatabaseConnection, LoggingTransaction
 from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine, Sqlite3Engine
-from synapse.storage.schema import SCHEMA_COMPAT_VERSION, SCHEMA_VERSION
+from synapse.storage.schema import (
+    BACKGROUND_UPDATES_COMPAT_VERSION,
+    SCHEMA_COMPAT_VERSION,
+    SCHEMA_VERSION,
+)
 from synapse.storage.types import Cursor
 
 logger = logging.getLogger(__name__)
@@ -80,6 +84,9 @@ class _SchemaState:
     applied_deltas: Collection[str] = attr.ib(factory=tuple)
     """Any delta files for `current_version` which have already been applied"""
 
+    background_updates: Collection[Tuple[str, int]] = attr.ib(factory=tuple)
+    """Any (pending) updates in the `background_updates` table."""
+
     upgraded: bool = attr.ib(default=False)
     """Whether the current state was reached by applying deltas.
 
@@ -359,6 +366,7 @@ def _upgrade_existing_database(
     """
     if is_empty:
         assert not current_schema_state.applied_deltas
+        assert not current_schema_state.background_updates
     else:
         assert config
 
@@ -413,6 +421,24 @@ def _upgrade_existing_database(
         start_ver += 1
 
     logger.debug("applied_delta_files: %s", current_schema_state.applied_deltas)
+    logger.debug(
+        "pending background_updates: %s",
+        (name for name, ordering in current_schema_state.background_updates),
+    )
+
+    # Bail if there are any pending background updates from before the background schema compat version.
+    for update_name, ordering in sorted(
+        current_schema_state.background_updates, key=lambda b: b[1]
+    ):
+        # ordering is an int based on when the background update was added:
+        #
+        #   (schema version when added * 100) + (schema delta when added).
+        update_schema_version = ordering // 100
+        if update_schema_version < BACKGROUND_UPDATES_COMPAT_VERSION:
+            raise UpgradeDatabaseException(
+                "Database has old pending background updates for version %d: %s"
+                % (update_schema_version, update_name)
+            )
 
     if isinstance(database_engine, PostgresEngine):
         specific_engine_extension = ".postgres"
@@ -705,10 +731,14 @@ def _get_or_create_schema_state(
     )
     applied_deltas = tuple(d for d, in txn)
 
+    txn.execute("SELECT update_name, ordering FROM background_updates")
+    background_Updates = tuple(txn)
+
     return _SchemaState(
         current_version=current_version,
         compat_version=compat_version,
         applied_deltas=applied_deltas,
+        background_updates=background_Updates,
         upgraded=upgraded,
     )
 
diff --git a/synapse/storage/schema/__init__.py b/synapse/storage/schema/__init__.py
index 5b50bd66bc..3bf9eeeca9 100644
--- a/synapse/storage/schema/__init__.py
+++ b/synapse/storage/schema/__init__.py
@@ -133,3 +133,14 @@ SCHEMA_COMPAT_VERSION = (
 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.
 """
+
+BACKGROUND_UPDATES_COMPAT_VERSION = (
+    # The replace_stream_ordering_column from 6001 must have run.
+    61
+)
+"""Limit on how far the syanpse can be rolled forward without breaking db compat
+
+This value is checked on startup against any pending background updates. If there
+are any pending background updates less than BACKGROUND_UPDATES_COMPAT_VERSION, then
+Synapse will refuse to start.
+"""