diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index 4a59132bf3..0e430356cd 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -90,8 +90,10 @@ class BackgroundUpdater(object):
self._clock = hs.get_clock()
self.db = database
+ # if a background update is currently running, its name.
+ self._current_background_update = None # type: Optional[str]
+
self._background_update_performance = {}
- self._background_update_queue = []
self._background_update_handlers = {}
self._all_done = False
@@ -131,7 +133,7 @@ class BackgroundUpdater(object):
return True
# obviously, if we have things in our queue, we're not done.
- if self._background_update_queue:
+ if self._current_background_update:
return False
# otherwise, check if there are updates to be run. This is important,
@@ -152,11 +154,10 @@ class BackgroundUpdater(object):
async def has_completed_background_update(self, update_name) -> bool:
"""Check if the given background update has finished running.
"""
-
if self._all_done:
return True
- if update_name in self._background_update_queue:
+ if update_name == self._current_background_update:
return False
update_exists = await self.db.simple_select_one_onecol(
@@ -180,31 +181,49 @@ class BackgroundUpdater(object):
Returns:
True if there is no more work to do, otherwise False
"""
- if not self._background_update_queue:
- updates = await self.db.simple_select_list(
- "background_updates",
- keyvalues=None,
- retcols=("update_name", "depends_on"),
+
+ def get_background_updates_txn(txn):
+ txn.execute(
+ """
+ SELECT update_name, depends_on FROM background_updates
+ ORDER BY ordering, update_name
+ """
)
- in_flight = {update["update_name"] for update in updates}
- for update in updates:
- if update["depends_on"] not in in_flight:
- self._background_update_queue.append(update["update_name"])
+ return self.db.cursor_to_dict(txn)
- if not self._background_update_queue:
- # no work left to do
- return True
+ if not self._current_background_update:
+ all_pending_updates = await self.db.runInteraction(
+ "background_updates", get_background_updates_txn,
+ )
+ if not all_pending_updates:
+ # no work left to do
+ return True
+
+ # find the first update which isn't dependent on another one in the queue.
+ pending = {update["update_name"] for update in all_pending_updates}
+ for upd in all_pending_updates:
+ depends_on = upd["depends_on"]
+ if not depends_on or depends_on not in pending:
+ break
+ logger.info(
+ "Not starting on bg update %s until %s is done",
+ upd["update_name"],
+ depends_on,
+ )
+ else:
+ # if we get to the end of that for loop, there is a problem
+ raise Exception(
+ "Unable to find a background update which doesn't depend on "
+ "another: dependency cycle?"
+ )
- # pop from the front, and add back to the back
- update_name = self._background_update_queue.pop(0)
- self._background_update_queue.append(update_name)
+ self._current_background_update = upd["update_name"]
- res = await self._do_background_update(update_name, desired_duration_ms)
+ await self._do_background_update(desired_duration_ms)
return False
- async def _do_background_update(
- self, update_name: str, desired_duration_ms: float
- ) -> int:
+ async def _do_background_update(self, desired_duration_ms: float) -> int:
+ update_name = self._current_background_update
logger.info("Starting update batch on background update '%s'", update_name)
update_handler = self._background_update_handlers[update_name]
@@ -405,9 +424,12 @@ class BackgroundUpdater(object):
Returns:
A deferred that completes once the task is removed.
"""
- self._background_update_queue = [
- name for name in self._background_update_queue if name != update_name
- ]
+ if update_name != self._current_background_update:
+ raise Exception(
+ "Cannot end background update %s which isn't currently running"
+ % update_name
+ )
+ self._current_background_update = None
return self.db.simple_delete_one(
"background_updates", keyvalues={"update_name": update_name}
)
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 6cb7d4b922..1712932f31 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -29,7 +29,7 @@ logger = logging.getLogger(__name__)
# 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 = 57
+SCHEMA_VERSION = 58
dir_path = os.path.abspath(os.path.dirname(__file__))
diff --git a/synapse/storage/schema/delta/58/00background_update_ordering.sql b/synapse/storage/schema/delta/58/00background_update_ordering.sql
new file mode 100644
index 0000000000..02dae587cc
--- /dev/null
+++ b/synapse/storage/schema/delta/58/00background_update_ordering.sql
@@ -0,0 +1,19 @@
+/* Copyright 2020 The Matrix.org Foundation C.I.C
+ *
+ * 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 an "ordering" column to background_updates, which can be used to sort them
+ to achieve some level of consistency. */
+
+ALTER TABLE background_updates ADD COLUMN ordering INT NOT NULL DEFAULT 0;
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