# User Directory API Implementation

The user directory is currently maintained based on the 'visible' users on this particular server - i.e. ones which your account shares a room with, or who are present in a publicly viewable room present on the server.

The directory info is stored in various tables, which can (typically after DB corruption) get stale or out of sync. If this happens, for now the solution to fix it is to execute the SQL here and then restart synapse. This should then start a background task to flush the current tables and regenerate the directory.

## Data model

There are five relevant tables that collectively form the "user directory". Three of them track a master list of all the users we could search for. The last two (collectively called the "search tables") track who can see who.

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

- support users
- appservice users
- deactivated users

- `user_directory`. This contains the user_id, display name and avatar we'll return when you search the directory.

  - Because there's only one directory entry per user, it's important that we only ever put publicly visible names here. Otherwise we might leak a private 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 with different code paths to match.

  - 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.

- `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.

- `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.