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Minor drive-by state res clarifications #1042

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merged 9 commits into from
May 30, 2022
Merged

Minor drive-by state res clarifications #1042

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9455e69
Opinionated rewrite of unconflicted state map
Apr 29, 2022
4b5cc45
Define auth chain
Apr 29, 2022
44b4bd3
auth_events -> `auth_events`
DMRobertson May 2, 2022
a25c769
Clarify first step of state res
May 3, 2022
2950681
Changelog
May 25, 2022
8c4c09f
Rich's suggestions
DMRobertson May 29, 2022
8ab0634
Clarify conflicted state set?
May 30, 2022
8c49f00
consistently use auth events
May 30, 2022
b573c95
Rich's suggestion for the union bit
May 30, 2022
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1 change: 1 addition & 0 deletions changelogs/server_server/newsfragments/1042.clarification
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Clarify the meaning of "unconflicted state map" and "auth chain" in state res v2.
25 changes: 17 additions & 8 deletions content/rooms/fragments/v2-state-res.md
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Expand Up @@ -31,11 +31,20 @@ the `membership` is `leave` or `ban` and the `sender` does not match the
might remove someone's ability to do something in the room.

**Unconflicted state map and conflicted state set.**
The *unconflicted state map* is the state where the value of each key
exists and is the same in each state *S*<sub>*i*</sub>. The *conflicted
state set* is the set of all other state events. Note that the
unconflicted state map only has one event per `(event_type, state_key)`,
whereas the conflicted state set may have multiple events.
The key-value pairs across all state maps *S<sub>i</sub>* can be divided into
two collections. If a given key *K* is present in every *S<sub>i</sub>* with the
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is it obvious that K is a (event_type, state_key) pair, or is there a way we can make that obvious?

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It would be helpful if there was a phrase which meant (event_type, state_key). How about 8ab0634?

same value *V* in each state map, then the pair (*K*, *V*) belongs to the
*unconflicted state map*. Otherwise (*K*, *V*) belongs to the
*conflicted state set*.

Note that the unconflicted state map only has one event per `(event_type, state_key)`,
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... switching from K to (event_type, state_key) here is jarring without that context.

whereas the conflicted state set may associate multiple events to the same key.

**Auth chain.**
The *auth chain* of an event *E* is the set containing all of *E*'s auth events,
all of *their* authorising events, and so on recursively, stretching back to the
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possibly we should stick to the term "auth events" rather than switching to "authorising events" ?

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This is 8c49f00

start of the room. Put differently, these are the events reachable by walking
the graph induced by an event's `auth_events` links.

**Auth difference.**
The *auth difference* is calculated by first calculating the full auth
Expand Down Expand Up @@ -112,9 +121,9 @@ the auth event is not rejected.

The *resolution* of a set of states is obtained as follows:

1. Take all *power events* and any events in their auth chains,
recursively, that appear in the *full conflicted set* and order them
by the *reverse topological power ordering*.
1. Select all *power events* that appear in the *full conflicted set*. Compute
the union of their auth chains. Sort the union using the
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*reverse topological power ordering*.
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2. Apply the *iterative auth checks algorithm*, starting from the
*unconflicted state map*, to the list of events from the previous
step to get a partially resolved state.
Expand Down