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Diffstat (limited to 'docs/development/room-dag-concepts.md')
| -rw-r--r-- | docs/development/room-dag-concepts.md | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/docs/development/room-dag-concepts.md b/docs/development/room-dag-concepts.md index cbc7cf2949..5eed72bec6 100644 --- a/docs/development/room-dag-concepts.md +++ b/docs/development/room-dag-concepts.md @@ -38,15 +38,16 @@ Most-recent-in-time events in the DAG which are not referenced by any other even The forward extremities of a room are used as the `prev_events` when the next event is sent. -## Backward extremity +## Backwards extremity The current marker of where we have backfilled up to and will generally be the -`prev_events` of the oldest-in-time events we have in the DAG. This gives a starting point when -backfilling history. +oldest-in-time events we know of in the DAG. -When we persist a non-outlier event, we clear it as a backward extremity and set -all of its `prev_events` as the new backward extremities if they aren't already -persisted in the `events` table. +This is an event where we haven't fetched all of the `prev_events` for. + +Once we have fetched all of its `prev_events`, it's unmarked as a backwards +extremity (although we may have formed new backwards extremities from the prev +events during the backfilling process). ## Outliers @@ -55,7 +56,8 @@ We mark an event as an `outlier` when we haven't figured out the state for the room at that point in the DAG yet. We won't *necessarily* have the `prev_events` of an `outlier` in the database, -but it's entirely possible that we *might*. +but it's entirely possible that we *might*. The status of whether we have all of +the `prev_events` is marked as a [backwards extremity](#backwards-extremity). For example, when we fetch the event auth chain or state for a given event, we mark all of those claimed auth events as outliers because we haven't done the |