Add Synapse Maintenance docs and synapse-janitor integration

docs/README.md

@@ -20,6 +20,8 @@
 
 - [Maintenance / upgrading services](maintenance-upgrading-services.md)
 
+- [Maintenance / Synapse](maintenance-synapse.md)
+
 - [Maintenance / PostgreSQL](maintenance-postgres.md)
 
 - [Maintenance and Troubleshooting](maintenance-and-troubleshooting.md)

docs/maintenance-postgres.md

@@ -6,6 +6,8 @@ Table of contents:
 
 - [Getting a database terminal](#getting-a-database-terminal), for when you wish to execute SQL queries
 
+- [Vacuuming PostgreSQL](#vacuuming-postgresql), for when you wish to run a Postgres [VACUUM](https://www.postgresql.org/docs/current/sql-vacuum.html) (optimizing disk space)
+
 - [Backing up PostgreSQL](#backing-up-postgresql), for when you wish to make a backup
 
 - [Upgrading PostgreSQL](#upgrading-postgresql), for upgrading to new major versions of PostgreSQL. Such **manual upgrades are sometimes required**.
@@ -18,6 +20,19 @@ You can use the `/usr/local/bin/matrix-postgres-cli` tool to get interactive ter
 If you are using an [external Postgres server](configuring-playbook-external-postgres.md), the above tool will not be available.
 
 
+## Vacuuming PostgreSQL
+
+To perform a `FULL` Postgres [VACUUM](https://www.postgresql.org/docs/current/sql-vacuum.html), run the playbook with `--tags=run-postgres-vacuum`.
+
+Example:
+
+```bash
+ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-vacuum
+```
+
+**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`).
+
+
 ## Backing up PostgreSQL
 
 To make a back up of the current PostgreSQL database, make sure it's running and then execute a command like this on the server:

docs/maintenance-synapse.md

@@ -0,0 +1,72 @@
+# 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](#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](#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](#compressing-state-with-rust-synapse-compress-state), for when you wish to compress some Synapse state tables using the [rust-synapse-compress-state](https://github.com/matrix-org/rust-synapse-compress-state) tool
+
+
+## Purging unused data with synapse-janitor
+
+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](https://github.com/xwiki-labs/synapse_scripts)), which are meant to solve this problem.
+
+To ask the playbook to run synapse-janitor, execute:
+
+```bash
+ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-synapse-janitor
+```
+
+**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`](./maintenance-postgres.md#vacuuming-postgresql).
+
+It's easiest if you ask the playbook to run both synapse-janitor and a `VACUUM FULL` in one call:
+
+```bash
+ansible-playbook -i inventory/hosts setup.yml --tags=run-postgres-synapse-janitor,run-postgres-vacuum
+```
+
+**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](#purging-unused-data-with-synapse-janitor) 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](https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_history_api.rst) 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](https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_history_api.rst) documentation page for the actual purging instructions.
+
+Don't forget that disk space only ever gets released after a [`FULL` Postgres `VACUUM`](./maintenance-postgres.md#vacuuming-postgresql) - something the playbook can help you with.
+
+
+## Compressing state with rust-synapse-compress-state
+
+[rust-synapse-compress-state](https://github.com/matrix-org/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](./docs/maintenance-postgres.md#backing-up-postgresql) first.