matrix-docker-ansible-deploy/docs/maintenance-synapse.md

Synapse maintenance

This document shows you how to perform various maintenance tasks related to the Synapse chat server.

Table of contents:

• Purging old data with the Purge History API, for when you wish to delete in-use (but old) data from the Synapse database

• Compressing state with rust-synapse-compress-state

• Browse and manipulate the database, for when you really need to take matters into your own hands

• Make Synapse faster

Purging old data with the Purge History API

You can use the Purge History API to delete in-use (but old) data.

This is destructive (especially for non-federated rooms), because it means people will no longer have access to history past a certain point.

Synapse's Purge History API can be used to purge on a per-room basis.

To make use of this API, you'll need an admin access token first. You can find your access token in the setting of some clients (like Element). Alternatively, you can log in and obtain a new access token like this:

curl \
--data '{"identifier": {"type": "m.id.user", "user": "YOUR_MATRIX_USERNAME" }, "password": "YOUR_MATRIX_PASSWORD", "type": "m.login.password", "device_id": "Synapse-Purge-History-API"}' \
https://matrix.DOMAIN/_matrix/client/r0/login

Follow the Purge History API documentation page for the actual purging instructions.

After deleting data, you may wish to run a FULL Postgres VACUUM.

Compressing state with rust-synapse-compress-state

rust-synapse-compress-state can be used to optimize some _state tables used by Synapse.

This tool should be safe to use (even when Synapse is running), but it's always a good idea to make Postgres backups first.

To ask the playbook to run rust-synapse-compress-state, execute:

ansible-playbook -i inventory/hosts setup.yml --tags=rust-synapse-compress-state

By default, all rooms with more than 100000 state group rows will be compressed. If you need to adjust this, pass: --extra-vars='matrix_synapse_rust_synapse_compress_state_min_state_groups_required=SOME_NUMBER_HERE' to the command above.

After state compression, you may wish to run a FULL Postgres VACUUM.

Browse and manipulate the database

When the matrix admin API and the other tools do not provide a more convenient way, having a look at synapse's postgresql database can satisfy a lot of admins' needs. First, set up an SSH tunnel to your matrix server (skip if it is your local machine):

# you may replace 1799 with an arbitrary port unbound on both machines
ssh -L 1799:localhost:1799 matrix.DOMAIN

Then start up an ephemeral adminer container on the Matrix server, connecting it to the matrix network and linking the postgresql container:

docker run --rm --publish 1799:8080 --link matrix-postgres --net matrix adminer

You should then be able to browse the adminer database administration GUI at http://localhost:1799/ after entering your DB credentials (found in the host_vars or on the server in {{matrix_synapse_config_dir_path}}/homeserver.yaml under database.args)

⚠️ Be very careful with this, there is no undo for impromptu DB operations.

Make Synapse faster

Synapse's presence feature which tracks which users are online and which are offline can use a lot of processing power. You can disable presence by adding matrix_synapse_use_presence: false to your vars.yml file.

Tuning Synapse's cache factor can help reduce RAM usage. See the upstream documentation for more information on what value to set the cache factor to. Use the variable matrix_synapse_caches_global_factor to set the cache factor.

Tuning your PostgreSQL database will also make Synapse run significantly faster. See maintenance-postgres.md##tuning-postgresql.

See also How do I optimize this setup for a low-power server?.