Synapse maintenance

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

Table of contents:

Purging unused data with synapse-janitor, for when you wish to delete unused data from the Synapse database
Purging old data with the Purge History API, for when you wish to delete in-use (but old) data from the Synapse database
Synapse maintenance
Browse and manipulate the database, for when you really need to take matters into your own hands

Purging unused data with synapse-janitor

NOTE: There are reports that synapse-janitor is dangerous to use and causes database corruption. You may wish to refrain from using it.

When you leave and forget a room, Synapse can clean up its data, but currently doesn't. This unused and unreachable data remains in your database forever.

There are external tools (like synapse-janitor), which are meant to solve this problem.

To ask the playbook to run synapse-janitor, execute:

ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-synapse-janitor,start

Note: this will automatically stop Synapse temporarily and restart it later.

Vacuuming Postgres

Running synapse-janitor potentially deletes a lot of data from the Postgres database. However, disk space only ever gets released after a FULL Postgres VACUUM.

It's easiest if you ask the playbook to run both synapse-janitor and a VACUUM FULL in one call:

ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-synapse-janitor,run-postgres-vacuum,start

Note: this will automatically stop Synapse temporarily and restart it later. You'll also need plenty of available disk space in your Postgres data directory (usually /matrix/postgres/data).

Purging old data with the Purge History API

If purging unused and unreachable data is not enough for you, you can start deleting 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 provides a Purge History API that you can use 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 riot-web). 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.

Don't forget that disk space only ever gets released after a FULL Postgres VACUUM - something the playbook can help you with.

Compressing state with rust-synapse-compress-state

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

Unfortunately, at this time the playbook can't help you run this experimental tool.

Since it's also experimental, you may wish to stay away from it, or at least make Postgres backups first.

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, connecting it to the matrix-net 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.

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