Number of room members sometimes incorrect

[bones-was-here]

Background information

• Dendrite version or git SHA: 0.8.7
• Monolith or Polylith?: monolith
• SQLite3 or Postgres?: postgres
• Running in Docker?: no
• go version: 1.17.10
• Client used (if applicable): element web & android

Description

• What is the problem: The number of member accounts counted for a room may be higher or lower than the real number (and inconsistent with matrix.org).
• Who is affected:
• How is this bug manifesting: The spaces summary and "room info" panel both show the same incorrect number.
• When did this first appear: Not sure it has ever worked reliably.

Steps to reproduce

I don't know how to reproduce reliably. Some rooms have the correct user number, some are out by 1 or 2, others by a lot.
#dendrite:matrix.org often differs by > 100.
Recently when a new (dendrite) user joined 2 existing rooms, the user count suddenly dropped. One room now is shown with 0 people, the other has 1, but both rooms still have about 20 people in them.

[neilalexander]

When this happens, does the actual member list also have lots of missing users, or is there an obvious disconnect between the users in the member list and the membership count?

[bones-was-here]

I'm pretty sure it's only the count that's wrong and the member list is right, certainly that's the case for the smaller rooms where I can count the users myself and get ~20 whereas dendrite counts 0 or 1.

The room with 0 is still listed in spaces summaries (despite #2504 (comment) - rooms are reliably not listed in spaces summaries for me if there's no users from the current homeserver in that room), so dendrite does consider that room to have members for that code path.

[S7evinK]

Hopefully this is fixed now, if not, feel free to reopen.

[bones-was-here]

I havn't seen the 0 users bug again (so far), but our main room still shows too many users (+12) and #dendrite:matrix.org and #dendrite-dev:matrix.org both show 2 users less on dendrite than on matrix.org (this is much closer than it used to be).

[bones-was-here]

I was able to fix all remaining user count discrepancies with the downloadState admin API feature.