User Directory API Implementation

The user directory is maintained based on users that are 'visible' to the homeserver - i.e. ones which are local to the server and ones which any local user shares a room with.

The directory info is stored in various tables, which can sometimes get out of sync (although this is considered a bug). If this happens, for now the solution to fix it is to use the admin API and execute the job regenerate_directory. This should then start a background task to flush the current tables and regenerate the directory. Depending on the size of your homeserver (number of users and rooms) this can take a while.

Data model

There are five relevant tables that collectively form the "user directory". Three of them track a list of all known users. The last two (collectively called the "search tables") track which users are visible to each other.

From all of these tables we exclude three types of local user:

  • support users
  • appservice users
  • deactivated users

A description of each table follows:

  • user_directory. This contains the user ID, display name and avatar of each user.

    • Because there is only one directory entry per user, it is important that it only contain publicly visible information. Otherwise, this will leak the nickname or avatar used in a private room.
    • Indexed on rooms. Indexed on users.

  • user_directory_search. To be joined to user_directory. It contains an extra column that enables full text search based on user IDs and display names. Different schemas for SQLite and Postgres are used.

    • Indexed on the full text search data. Indexed on users.

  • user_directory_stream_pos. When the initial background update to populate the directory is complete, we record a stream position here. This indicates that synapse should now listen for room changes and incrementally update the directory where necessary. (See stream positions.)

  • users_in_public_rooms. Contains associations between users and the public rooms they're in. Used to determine which users are in public rooms and should be publicly visible in the directory. Both local and remote users are tracked.

  • users_who_share_private_rooms. Rows are triples (L, M, room id) where L is a local user and M is a local or remote user. L and M should be different, but this isn't enforced by a constraint.

    Note that if two local users share a room then there will be two entries: (user1, user2, !room_id) and (user2, user1, !room_id).

Configuration options

The exact way user search works can be tweaked via some server-level configuration options.

The information is not repeated here, but the options are mentioned below.

Search algorithm

If search_all_users is false, then results are limited to users who:

  1. Are found in the users_in_public_rooms table, or
  2. Are found in the users_who_share_private_rooms where L is the requesting user and M is the search result.

Otherwise, if search_all_users is true, no such limits are placed and all users known to the server (matching the search query) will be returned.

By default, locked users are not returned. If show_locked_users is true then no filtering on the locked status of a user is done.

The user provided search term is lowercased and normalized using NFKC, this treats the string as case-insensitive, canonicalizes different forms of the same text, and maps some "roughly equivalent" characters together.

The search term is then split into words:

  • If ICU is available, then the system's default locale will be used to break the search term into words. (See the installation instructions for how to install ICU.)
  • If unavailable, then runs of ASCII characters, numbers, underscores, and hypens are considered words.

The queries for PostgreSQL and SQLite are detailed below, by their overall goal is to find matching users, preferring users who are "real" (e.g. not bots, not deactivated). It is assumed that real users will have an display name and avatar set.

PostgreSQL

The above words are then transformed into two queries:

  1. "exact" which matches the parsed words exactly (using to_tsquery);
  2. "prefix" which matches the parsed words as prefixes (using to_tsquery).

Results are composed of all rows in the user_directory_search table whose information matches one (or both) of these queries. Results are ordered by calculating a weighted score for each result, higher scores are returned first:

  • 4x if a user ID exists.
  • 1.2x if the user has a display name set.
  • 1.2x if the user has an avatar set.
  • 0x-3x by the full text search results using the ts_rank_cd function against the "exact" search query; this has four variables with the following weightings:
    • D: 0.1 for the user ID's domain
    • C: 0.1 for unused
    • B: 0.9 for the user's display name (or an empty string if it is not set)
    • A: 0.1 for the user ID's localpart
  • 0x-1x by the full text search results using the ts_rank_cd function against the "prefix" search query. (Using the same weightings as above.)
  • If prefer_local_users is true, then 2x if the user is local to the homeserver.

Note that ts_rank_cd returns a weight between 0 and 1. The initial weighting of all results is 1.

SQLite

Results are composed of all rows in the user_directory_search whose information matches the query. Results are ordered by the following information, with each subsequent column used as a tiebreaker, for each result:

  1. By the rank of the full text search results using the matchinfo function. Higher ranks are returned first.
  2. If prefer_local_users is true, then users local to the homeserver are returned first.
  3. Users with a display name set are returned first.
  4. Users with an avatar set are returned first.