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MadLittleMods
2022-09-02 19:06:22 +00:00
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@@ -308,6 +308,22 @@ default value is the <strong>string</strong> <code>&quot;FALSE&quot;</code> - wh
in Python, evaluates to <code>True</code>.</p>
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<h2 id="event_id-global-uniqueness"><a class="header" href="#event_id-global-uniqueness"><code>event_id</code> global uniqueness</a></h2>
<p>In room versions <code>1</code> and <code>2</code> it's possible to end up with two events with the
same <code>event_id</code> (in the same or different rooms). After room version <code>3</code>, that
can only happen with a hash collision, which we basically hope will never
happen.</p>
<p>There are several places in Synapse and even Matrix APIs like <a href="https://spec.matrix.org/v1.1/server-server-api/#get_matrixfederationv1eventeventid"><code>GET /_matrix/federation/v1/event/{eventId}</code></a>
where we assume that event IDs are globally unique.</p>
<p>But hash collisions are still possible, and by treating event IDs as room
scoped, we can reduce the possibility of a hash collision. When scoping
<code>event_id</code> in the database schema, it should be also accompanied by <code>room_id</code>
(<code>PRIMARY KEY (room_id, event_id)</code>) and lookups should be done through the pair
<code>(room_id, event_id)</code>.</p>
<p>There has been a lot of debate on this in places like
https://github.com/matrix-org/matrix-spec-proposals/issues/2779 and
<a href="https://github.com/matrix-org/matrix-spec-proposals/pull/2848">MSC2848</a> which
has no resolution yet (as of 2022-09-01).</p>
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