Store whether a BG update is oneshot or not

synapse/storage/background_updates.py

@@ -14,6 +14,8 @@
 import logging
 from typing import TYPE_CHECKING, Awaitable, Callable, Dict, Iterable, Optional
 
+import attr
+
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.types import Connection
 from synapse.types import JsonDict
@@ -28,6 +30,22 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class _BackgroundUpdateHandler:
+    """A handler for a given background update.
+
+    Attributes:
+        callback: The function to call to make progress on the background
+            update.
+        oneshot: Wether the update is likely to happen all in one go, ignoring
+            the supplied target duration, e.g. index creation. This is used by
+            the update controller to help correctly schedule the update.
+    """
+
+    callback: Callable[[JsonDict, int], Awaitable[int]]
+    oneshot: bool = False
+
+
 class BackgroundUpdatePerformance:
     """Tracks the how long a background update is taking to update its items"""
 
@@ -95,9 +113,7 @@ class BackgroundUpdater:
         self._current_background_update: Optional[str] = None
 
         self._background_update_performance: Dict[str, BackgroundUpdatePerformance] = {}
-        self._background_update_handlers: Dict[
-            str, Callable[[JsonDict, int], Awaitable[int]]
-        ] = {}
+        self._background_update_handlers: Dict[str, _BackgroundUpdateHandler] = {}
         self._all_done = False
 
         # Whether we're currently running updates
@@ -258,7 +274,7 @@ class BackgroundUpdater:
         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]
+        update_handler = self._background_update_handlers[update_name].callback
 
         performance = self._background_update_performance.get(update_name)
 
@@ -329,7 +345,9 @@ class BackgroundUpdater:
             update_name: The name of the update that this code handles.
             update_handler: The function that does the update.
         """
-        self._background_update_handlers[update_name] = update_handler
+        self._background_update_handlers[update_name] = _BackgroundUpdateHandler(
+            update_handler
+        )
 
     def register_noop_background_update(self, update_name: str) -> None:
         """Register a noop handler for a background update.
@@ -451,7 +469,9 @@ class BackgroundUpdater:
             await self._end_background_update(update_name)
             return 1
 
-        self.register_background_update_handler(update_name, updater)
+        self._background_update_handlers[update_name] = _BackgroundUpdateHandler(
+            updater, oneshot=True
+        )
 
     async def _end_background_update(self, update_name: str) -> None:
         """Removes a completed background update task from the queue.