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105 lines
7.4 KiB
Markdown
105 lines
7.4 KiB
Markdown
# Synapse maintenance
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This document shows you how to perform various maintenance tasks related to the Synapse chat server.
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Table of contents:
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- [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
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- [Compressing state with rust-synapse-compress-state](#compressing-state-with-rust-synapse-compress-state)
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- [Browse and manipulate the database](#browse-and-manipulate-the-database), for when you really need to take matters into your own hands
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- [Make Synapse faster](#make-synapse-faster)
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## Purging old data with the Purge History API
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You can use the **[Purge History API](https://github.com/element-hq/synapse/blob/master/docs/admin_api/purge_history_api.md)** to delete old messages on a per-room basis. **This is destructive** (especially for non-federated rooms), because it means **people will no longer have access to history past a certain point**.
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To make use of this Synapse Admin API, **you'll need an admin access token** first. Refer to the documentation on [how to obtain an access token](obtaining-access-tokens.md).
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Synapse's Admin API is not exposed to the internet by default, following [official Synapse reverse-proxying recommendations](https://github.com/element-hq/synapse/blob/master/docs/reverse_proxy.md#synapse-administration-endpoints). To expose it you will need to add `matrix_synapse_container_labels_public_client_synapse_admin_api_enabled: true` to your `vars.yml` file.
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Follow the [Purge History API](https://github.com/element-hq/synapse/blob/master/docs/admin_api/purge_history_api.md) documentation page for the actual purging instructions.
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After deleting data, you may wish to run a [`FULL` Postgres `VACUUM`](./maintenance-postgres.md#vacuuming-postgresql).
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## Compressing state with rust-synapse-compress-state
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[rust-synapse-compress-state](https://github.com/matrix-org/rust-synapse-compress-state) can be used to optimize some `_state` tables used by Synapse. If your server participates in large rooms this is the most effective way to reduce the size of your database.
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**Note**: besides running the `rust-synapse-compress-state` tool manually, you can also enable its `synapse-auto-compressor` tool by [Setting up synapse-auto-compressor](configuring-playbook-synapse-auto-compressor.md). The automatic tool will run on a schedule every day and you won't have to compress state manually ever again.
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`rust-synapse-compress-state` should be safe to use (even when Synapse is running), but it's always a good idea to [make Postgres backups](./maintenance-postgres.md#backing-up-postgresql) first.
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To ask the playbook to run rust-synapse-compress-state, execute:
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```
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ansible-playbook -i inventory/hosts setup.yml --tags=rust-synapse-compress-state
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```
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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.
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After state compression, you may wish to run a [`FULL` Postgres `VACUUM`](./maintenance-postgres.md#vacuuming-postgresql).
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## Browse and manipulate the database
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When the [Synapse Admin API](https://github.com/element-hq/synapse/tree/master/docs/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.
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Editing the database manually is not recommended or supported by the Synapse developers. If you are going to do so you should [make a database backup](./maintenance-postgres.md#backing-up-postgresql).
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First, set up an SSH tunnel to your Matrix server (skip if it is your local machine):
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```
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# you may replace 1799 with an arbitrary port unbound on both machines
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ssh -L 1799:localhost:1799 matrix.example.com
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```
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Then start up an ephemeral [adminer](https://www.adminer.org/) container on the Matrix server, connecting it to the `matrix` network and linking the postgresql container:
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```
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docker run --rm --publish 1799:8080 --link matrix-postgres --net matrix adminer
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```
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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`)
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⚠️ Be **very careful** with this, there is **no undo** for impromptu DB operations.
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## Make Synapse faster
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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_presence_enabled: false` to your `vars.yml` file.
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If you have enough compute resources (CPU & RAM), you can make Synapse better use of them by [enabling load-balancing with workers](configuring-playbook-synapse.md#load-balancing-with-workers).
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[Tuning your PostgreSQL database](maintenance-postgres.md#tuning-postgresql) could also improve Synapse performance. The playbook tunes the integrated Postgres database automatically, but based on your needs you may wish to adjust tuning variables manually. If you're using an [external Postgres database](configuring-playbook-external-postgres.md), you will also need to tune Postgres manually.
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### Tuning caches and cache autotuning
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Tuning Synapse's cache factor is useful for performance increases but also as part of controlling Synapse's memory use. Use the variable `matrix_synapse_caches_global_factor` to set the cache factor as part of this process.
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**The playbook defaults the global cache factor to a large value** (e.g. `10`). A smaller value (e.g. `0.5`) will decrease the amount used for caches, but will [not necessarily decrease RAM usage as a whole](https://github.com/matrix-org/synapse/issues/3939).
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Tuning the cache factor is useful only to a limited degree (as its crude to do in isolation) and therefore users who are tuning their cache factor should likely look into tuning autotune variables as well (see below).
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Cache autotuning is **enabled by default** and controlled via the following variables:
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- `matrix_synapse_cache_autotuning_max_cache_memory_usage` - defaults to 1/8 of total RAM with a cap of 2GB; values are specified in bytes
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- `matrix_synapse_cache_autotuning_target_cache_memory_usage` - defaults to 1/16 of total RAM with a cap of 1GB; values are specified in bytes
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- `matrix_synapse_cache_autotuning_min_cache_ttl` - defaults to `30s`
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You can **learn more about cache-autotuning and the global cache factor settings** in the [Synapse's documentation on caches and associated values](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#caches-and-associated-values).
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To **disable cache auto-tuning**, unset all values:
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```yml
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matrix_synapse_cache_autotuning_max_cache_memory_usage: ''
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matrix_synapse_cache_autotuning_target_cache_memory_usage: ''
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matrix_synapse_cache_autotuning_min_cache_ttl: ''
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```
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Users who wish to lower Synapse's RAM footprint should look into lowering the global cache factor and tweaking the autotune variables (or disabling auto-tuning). If your cache factor is too low for a given auto tune setting your caches will not reach autotune thresholds and autotune won't be able to do its job. Therefore, when auto-tuning is enabled (which it is by default), it's recommended to have your cache factor be large.
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See also [How do I optimize this setup for a low-power server?](faq.md#how-do-i-optimize-this-setup-for-a-low-power-server).
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