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Olivier 'reivilibreandEric Eastwood 7773f05596 Use sharded tokens in MSC4354: Sticky Events sync and sliding sync, preventing events appearing in multiple sync responses. (#20186 )

Fixes: #19661
Part of: MSC4354

First introduced some helpers for querying a sharded stream, which were moved to
https://github.com/element-hq/synapse/pull/20108.

- SQL builder for 'give me rows between two sharded tokens'
- a function to return the 'new' from_token after a limited read


Then make the sticky events portions of both oldschool and sliding sync use
sharded tokens.

This prevents a 'torn sync' problem where, because the events and sticky
events streams are both sharded with the same writers:

1. persisting a sticky event leads to an event row and a `sticky_events`
row being created for event `e` (on writer `W`).
2. Suppose another writer is still persisting, so the position of the
stream for writer W advances, but the global
['linear'](https://element-hq.github.io/synapse/latest/development/synapse_architecture/streams.html?highlight=%E2%80%9Clinear%E2%80%9D#current-stream-id)
(I have been calling this 'baseline') position does not advance yet.
3. sync is sharding-aware for the regular events stream, so `e` appears
as a real-time timeline event, thus coming down sync
4. since sticky events were not sharding-aware, `e` is not detected as a
sticky event in this sync response. The sticky event position doesn't
advance in the sync token, either.
5. (assume the position advances because other writers have finished
writing and so the 'linear' position advances for the sticky events
stream)
6. the client then syncs again, using the new sync token. This time, `e`
appears in the sticky event section.

If we make sticky events sharding-aware in sync, then `e` would appear
for consideration in both the timeline section **and** the sticky event
section in the first sync.
It then gets deduplicated out of the sticky section since it is
appearing in the timeline section in the same sync.

---------

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>
Co-authored-by: Eric Eastwood <erice@element.io>

2026-10-05 12:40:55 +01:00

http

Rename the test_disconnect test helper so that pytest doesn't see it as a test. (#19486 )

2026-02-20 15:37:34 +00:00

storage

Port Event class to Rust (#19701 )

2026-06-02 11:05:38 +01:00

tcp

Fix state events missing from MSC4222 state_after when the since token falls inside a persist batch (#20171 )

2026-09-16 11:07:25 +02:00

__init__.py

Correctly mention previous copyright (#16820 )