diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 360ab6fee2..500c1c16d0 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -38,7 +38,7 @@ from signedjson.sign import verify_signed_json
from unpaddedbase64 import decode_base64
from synapse import event_auth
-from synapse.api.constants import EventContentFields, EventTypes, Membership
+from synapse.api.constants import MAX_DEPTH, EventContentFields, EventTypes, Membership
from synapse.api.errors import (
AuthError,
CodeMessageException,
@@ -211,7 +211,7 @@ class FederationHandler:
current_depth: int,
limit: int,
*,
- processing_start_time: int,
+ processing_start_time: Optional[int],
) -> bool:
"""
Checks whether the `current_depth` is at or approaching any backfill
@@ -223,12 +223,23 @@ class FederationHandler:
room_id: The room to backfill in.
current_depth: The depth to check at for any upcoming backfill points.
limit: The max number of events to request from the remote federated server.
- processing_start_time: The time when `maybe_backfill` started
- processing. Only used for timing.
+ processing_start_time: The time when `maybe_backfill` started processing.
+ Only used for timing. If `None`, no timing observation will be made.
"""
backwards_extremities = [
_BackfillPoint(event_id, depth, _BackfillPointType.BACKWARDS_EXTREMITY)
- for event_id, depth in await self.store.get_backfill_points_in_room(room_id)
+ for event_id, depth in await self.store.get_backfill_points_in_room(
+ room_id=room_id,
+ current_depth=current_depth,
+ # We only need to end up with 5 extremities combined with the
+ # insertion event extremities to make the `/backfill` request
+ # but fetch an order of magnitude more to make sure there is
+ # enough even after we filter them by whether visible in the
+ # history. This isn't fool-proof as all backfill points within
+ # our limit could be filtered out but seems like a good amount
+ # to try with at least.
+ limit=50,
+ )
]
insertion_events_to_be_backfilled: List[_BackfillPoint] = []
@@ -236,7 +247,12 @@ class FederationHandler:
insertion_events_to_be_backfilled = [
_BackfillPoint(event_id, depth, _BackfillPointType.INSERTION_PONT)
for event_id, depth in await self.store.get_insertion_event_backward_extremities_in_room(
- room_id
+ room_id=room_id,
+ current_depth=current_depth,
+ # We only need to end up with 5 extremities combined with
+ # the backfill points to make the `/backfill` request ...
+ # (see the other comment above for more context).
+ limit=50,
)
]
logger.debug(
@@ -245,10 +261,6 @@ class FederationHandler:
insertion_events_to_be_backfilled,
)
- if not backwards_extremities and not insertion_events_to_be_backfilled:
- logger.debug("Not backfilling as no extremeties found.")
- return False
-
# we now have a list of potential places to backpaginate from. We prefer to
# start with the most recent (ie, max depth), so let's sort the list.
sorted_backfill_points: List[_BackfillPoint] = sorted(
@@ -269,6 +281,33 @@ class FederationHandler:
sorted_backfill_points,
)
+ # If we have no backfill points lower than the `current_depth` then
+ # either we can a) bail or b) still attempt to backfill. We opt to try
+ # backfilling anyway just in case we do get relevant events.
+ if not sorted_backfill_points and current_depth != MAX_DEPTH:
+ logger.debug(
+ "_maybe_backfill_inner: all backfill points are *after* current depth. Trying again with later backfill points."
+ )
+ return await self._maybe_backfill_inner(
+ room_id=room_id,
+ # We use `MAX_DEPTH` so that we find all backfill points next
+ # time (all events are below the `MAX_DEPTH`)
+ current_depth=MAX_DEPTH,
+ limit=limit,
+ # We don't want to start another timing observation from this
+ # nested recursive call. The top-most call can record the time
+ # overall otherwise the smaller one will throw off the results.
+ processing_start_time=None,
+ )
+
+ # Even after recursing with `MAX_DEPTH`, we didn't find any
+ # backward extremities to backfill from.
+ if not sorted_backfill_points:
+ logger.debug(
+ "_maybe_backfill_inner: Not backfilling as no backward extremeties found."
+ )
+ return False
+
# If we're approaching an extremity we trigger a backfill, otherwise we
# no-op.
#
@@ -278,47 +317,16 @@ class FederationHandler:
# chose more than one times the limit in case of failure, but choosing a
# much larger factor will result in triggering a backfill request much
# earlier than necessary.
- #
- # XXX: shouldn't we do this *after* the filter by depth below? Again, we don't
- # care about events that have happened after our current position.
- #
- max_depth = sorted_backfill_points[0].depth
- if current_depth - 2 * limit > max_depth:
+ max_depth_of_backfill_points = sorted_backfill_points[0].depth
+ if current_depth - 2 * limit > max_depth_of_backfill_points:
logger.debug(
"Not backfilling as we don't need to. %d < %d - 2 * %d",
- max_depth,
+ max_depth_of_backfill_points,
current_depth,
limit,
)
return False
- # We ignore extremities that have a greater depth than our current depth
- # as:
- # 1. we don't really care about getting events that have happened
- # after our current position; and
- # 2. we have likely previously tried and failed to backfill from that
- # extremity, so to avoid getting "stuck" requesting the same
- # backfill repeatedly we drop those extremities.
- #
- # However, we need to check that the filtered extremities are non-empty.
- # If they are empty then either we can a) bail or b) still attempt to
- # backfill. We opt to try backfilling anyway just in case we do get
- # relevant events.
- #
- filtered_sorted_backfill_points = [
- t for t in sorted_backfill_points if t.depth <= current_depth
- ]
- if filtered_sorted_backfill_points:
- logger.debug(
- "_maybe_backfill_inner: backfill points before current depth: %s",
- filtered_sorted_backfill_points,
- )
- sorted_backfill_points = filtered_sorted_backfill_points
- else:
- logger.debug(
- "_maybe_backfill_inner: all backfill points are *after* current depth. Backfilling anyway."
- )
-
# For performance's sake, we only want to paginate from a particular extremity
# if we can actually see the events we'll get. Otherwise, we'd just spend a lot
# of resources to get redacted events. We check each extremity in turn and
@@ -452,10 +460,15 @@ class FederationHandler:
return False
- processing_end_time = self.clock.time_msec()
- backfill_processing_before_timer.observe(
- (processing_end_time - processing_start_time) / 1000
- )
+ # If we have the `processing_start_time`, then we can make an
+ # observation. We wouldn't have the `processing_start_time` in the case
+ # where `_maybe_backfill_inner` is recursively called to find any
+ # backfill points regardless of `current_depth`.
+ if processing_start_time is not None:
+ processing_end_time = self.clock.time_msec()
+ backfill_processing_before_timer.observe(
+ (processing_end_time - processing_start_time) / 1000
+ )
success = await try_backfill(likely_domains)
if success:
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py
index 3251fca6fb..17f2fd4458 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -726,17 +726,35 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
async def get_backfill_points_in_room(
self,
room_id: str,
+ current_depth: int,
+ limit: int,
) -> List[Tuple[str, int]]:
"""
- Gets the oldest events(backwards extremities) in the room along with the
- approximate depth. Sorted by depth, highest to lowest (descending).
+ Get the backward extremities to backfill from in the room along with the
+ approximate depth.
+
+ Only returns events that are at a depth lower than or
+ equal to the `current_depth`. Sorted by depth, highest to lowest (descending)
+ so the closest events to the `current_depth` are first in the list.
+
+ We ignore extremities that are newer than the user's current scroll position
+ (ie, those with depth greater than `current_depth`) as:
+ 1. we don't really care about getting events that have happened
+ after our current position; and
+ 2. by the nature of paginating and scrolling back, we have likely
+ previously tried and failed to backfill from that extremity, so
+ to avoid getting "stuck" requesting the same backfill repeatedly
+ we drop those extremities.
Args:
room_id: Room where we want to find the oldest events
+ current_depth: The depth at the user's current scrollback position
+ limit: The max number of backfill points to return
Returns:
List of (event_id, depth) tuples. Sorted by depth, highest to lowest
- (descending)
+ (descending) so the closest events to the `current_depth` are first
+ in the list.
"""
def get_backfill_points_in_room_txn(
@@ -785,6 +803,18 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
*/
AND edge.is_state is ? /* False */
/**
+ * We only want backwards extremities that are older than or at
+ * the same position of the given `current_depth` (where older
+ * means less than the given depth) because we're looking backwards
+ * from the `current_depth` when backfilling.
+ *
+ * current_depth (ignore events that come after this, ignore 2-4)
+ * |
+ * ▼
+ * <oldest-in-time> [0]<--[1]<--[2]<--[3]<--[4] <newest-in-time>
+ */
+ AND event.depth <= ? /* current_depth */
+ /**
* Exponential back-off (up to the upper bound) so we don't retry the
* same backfill point over and over. ex. 2hr, 4hr, 8hr, 16hr, etc.
*
@@ -798,11 +828,13 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
OR ? /* current_time */ >= failed_backfill_attempt_info.last_attempt_ts + /*least*/%s((1 << failed_backfill_attempt_info.num_attempts) * ? /* step */, ? /* upper bound */)
)
/**
- * Sort from highest to the lowest depth. Then tie-break on
- * alphabetical order of the event_ids so we get a consistent
- * ordering which is nice when asserting things in tests.
+ * Sort from highest (closest to the `current_depth`) to the lowest depth
+ * because the closest are most relevant to backfill from first.
+ * Then tie-break on alphabetical order of the event_ids so we get a
+ * consistent ordering which is nice when asserting things in tests.
*/
ORDER BY event.depth DESC, backward_extrem.event_id DESC
+ LIMIT ?
"""
if isinstance(self.database_engine, PostgresEngine):
@@ -817,9 +849,11 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
(
room_id,
False,
+ current_depth,
self._clock.time_msec(),
1000 * BACKFILL_EVENT_EXPONENTIAL_BACKOFF_STEP_SECONDS,
1000 * BACKFILL_EVENT_BACKOFF_UPPER_BOUND_SECONDS,
+ limit,
),
)
@@ -835,18 +869,34 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
async def get_insertion_event_backward_extremities_in_room(
self,
room_id: str,
+ current_depth: int,
+ limit: int,
) -> List[Tuple[str, int]]:
"""
Get the insertion events we know about that we haven't backfilled yet
- along with the approximate depth. Sorted by depth, highest to lowest
- (descending).
+ along with the approximate depth. Only returns insertion events that are
+ at a depth lower than or equal to the `current_depth`. Sorted by depth,
+ highest to lowest (descending) so the closest events to the
+ `current_depth` are first in the list.
+
+ We ignore insertion events that are newer than the user's current scroll
+ position (ie, those with depth greater than `current_depth`) as:
+ 1. we don't really care about getting events that have happened
+ after our current position; and
+ 2. by the nature of paginating and scrolling back, we have likely
+ previously tried and failed to backfill from that insertion event, so
+ to avoid getting "stuck" requesting the same backfill repeatedly
+ we drop those insertion event.
Args:
room_id: Room where we want to find the oldest events
+ current_depth: The depth at the user's current scrollback position
+ limit: The max number of insertion event extremities to return
Returns:
List of (event_id, depth) tuples. Sorted by depth, highest to lowest
- (descending)
+ (descending) so the closest events to the `current_depth` are first
+ in the list.
"""
def get_insertion_event_backward_extremities_in_room_txn(
@@ -870,6 +920,18 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
WHERE
insertion_event_extremity.room_id = ?
/**
+ * We only want extremities that are older than or at
+ * the same position of the given `current_depth` (where older
+ * means less than the given depth) because we're looking backwards
+ * from the `current_depth` when backfilling.
+ *
+ * current_depth (ignore events that come after this, ignore 2-4)
+ * |
+ * ▼
+ * <oldest-in-time> [0]<--[1]<--[2]<--[3]<--[4] <newest-in-time>
+ */
+ AND event.depth <= ? /* current_depth */
+ /**
* Exponential back-off (up to the upper bound) so we don't retry the
* same backfill point over and over. ex. 2hr, 4hr, 8hr, 16hr, etc
*
@@ -883,11 +945,13 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
OR ? /* current_time */ >= failed_backfill_attempt_info.last_attempt_ts + /*least*/%s((1 << failed_backfill_attempt_info.num_attempts) * ? /* step */, ? /* upper bound */)
)
/**
- * Sort from highest to the lowest depth. Then tie-break on
- * alphabetical order of the event_ids so we get a consistent
- * ordering which is nice when asserting things in tests.
+ * Sort from highest (closest to the `current_depth`) to the lowest depth
+ * because the closest are most relevant to backfill from first.
+ * Then tie-break on alphabetical order of the event_ids so we get a
+ * consistent ordering which is nice when asserting things in tests.
*/
ORDER BY event.depth DESC, insertion_event_extremity.event_id DESC
+ LIMIT ?
"""
if isinstance(self.database_engine, PostgresEngine):
@@ -901,9 +965,11 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
sql % (least_function,),
(
room_id,
+ current_depth,
self._clock.time_msec(),
1000 * BACKFILL_EVENT_EXPONENTIAL_BACKOFF_STEP_SECONDS,
1000 * BACKFILL_EVENT_BACKOFF_UPPER_BOUND_SECONDS,
+ limit,
),
)
return cast(List[Tuple[str, int]], txn.fetchall())
|
