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Reduce DB usage when backpaginating

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In certain cases going from a stream token to a topological token can be
expensive (as it all rows in the room above the stream ordering), so we
refactor things so we do that calculation less.
This commit is contained in:
Erik Johnston 2024-04-05 15:05:22 +01:00
parent 5360baeb64
commit c243916546
1 changed files with 21 additions and 10 deletions
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31
synapse/handlers/pagination.py
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@ -468,16 +468,6 @@ class PaginationHandler:
room_id, requester, allow_departed_users=True
)
if pagin_config.direction == Direction.BACKWARDS:
# if we're going backwards, we might need to backfill. This
# requires that we have a topo token.
if room_token.topological:
curr_topo = room_token.topological
else:
curr_topo = await self.store.get_current_topological_token(
room_id, room_token.stream
)
# If they have left the room then clamp the token to be before
# they left the room, to save the effort of loading from the
# database.
@ -496,6 +486,14 @@ class PaginationHandler:
)
assert leave_token.topological is not None
# We need the topological part of the token to compare against.
if room_token.topological:
curr_topo = room_token.topological
else:
curr_topo = await self.store.get_current_topological_token(
room_id, room_token.stream
)
if leave_token.topological < curr_topo:
from_token = from_token.copy_and_replace(
StreamKeyType.ROOM, leave_token
@ -561,6 +559,19 @@ class PaginationHandler:
break
previous_event_depth = event_depth
# if we're going backwards, we might need to backfill. This
# requires that we have a topo token.
if room_token.topological:
curr_topo = room_token.topological
elif events:
# If we've already fetched some events then we can just use
# those to get the right depth.
curr_topo = events[0].depth
else:
curr_topo = await self.store.get_current_topological_token(
room_id, room_token.stream
)
# Backfill in the foreground if we found a big gap, have too many holes,
# or we don't have enough events to fill the limit that the client asked
# for.