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Quentin Gliech
f18998e6ce
`event_push_summary` rows written by rotation for a room the user has never sent a receipt in have a NULL `last_receipt_stream_ordering`, and the badge queries read NULL as "already accounts for every receipt" -- a compatibility branch for rows written before Synapse v1.62.0. It is only sound while the user has no receipt: such a row counts from the user's join, so once a receipt arrives it may include events at or before it. A receipt for an event older than the row's high-water mark was therefore ignored until the next rotation, up to 30 seconds later, leaving a stale unread count. Only trust a NULL row while the user has no receipt covering the thread. The manual count from `event_push_actions` that replaces it can only be complete above the point `_remove_old_push_actions_that_have_rotated` deletes from, so below that we keep serving the (possibly stale) summary and let the next rotation correct it: distrusting the row there would drop the counts entirely rather than merely delay them. For the same reason, keep a row whose stamp cannot be reconciled with any receipt at all. With no unthreaded receipt the comparison is against the user's membership event, which a receipt from before their latest join can never match -- and nothing recalculates such a row, since the receipt is not new.