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Reference homeserver for the Matrix decentralised comms protocol

Project description


Matrix is an ambitious new ecosystem for open federated Instant Messaging and VoIP. The basics you need to know to get up and running are:

  • Everything in Matrix happens in a room. Rooms are distributed and do not exist on any single server. Rooms can be located using convenience aliases like or #test:localhost:8448.
  • Matrix user IDs look like (although in the future you will normally refer to yourself and others using a third party identifier (3PID): email address, phone number, etc rather than manipulating Matrix user IDs)

The overall architecture is:

client <----> homeserver <=====================> homeserver <----> client is the official support room for Matrix, and can be accessed by any client from or via IRC bridge at irc://

Synapse is currently in rapid development, but as of version 0.5 we believe it is sufficiently stable to be run as an internet-facing service for real usage!

About Matrix

Matrix specifies a set of pragmatic RESTful HTTP JSON APIs as an open standard, which handle:

  • Creating and managing fully distributed chat rooms with no single points of control or failure
  • Eventually-consistent cryptographically secure synchronisation of room state across a global open network of federated servers and services
  • Sending and receiving extensible messages in a room with (optional) end-to-end encryption[1]
  • Inviting, joining, leaving, kicking, banning room members
  • Managing user accounts (registration, login, logout)
  • Using 3rd Party IDs (3PIDs) such as email addresses, phone numbers, Facebook accounts to authenticate, identify and discover users on Matrix.
  • Placing 1:1 VoIP and Video calls

These APIs are intended to be implemented on a wide range of servers, services and clients, letting developers build messaging and VoIP functionality on top of the entirely open Matrix ecosystem rather than using closed or proprietary solutions. The hope is for Matrix to act as the building blocks for a new generation of fully open and interoperable messaging and VoIP apps for the internet.

Synapse is a reference “homeserver” implementation of Matrix from the core development team at, written in Python/Twisted. It is intended to showcase the concept of Matrix and let folks see the spec in the context of a codebase and let you run your own homeserver and generally help bootstrap the ecosystem.

In Matrix, every user runs one or more Matrix clients, which connect through to a Matrix homeserver. The homeserver stores all their personal chat history and user account information - much as a mail client connects through to an IMAP/SMTP server. Just like email, you can either run your own Matrix homeserver and control and own your own communications and history or use one hosted by someone else (e.g. - there is no single point of control or mandatory service provider in Matrix, unlike WhatsApp, Facebook, Hangouts, etc.

We’d like to invite you to join (via, run a homeserver, take a look at the Matrix spec, and experiment with the APIs and Client SDKs.

Thanks for using Matrix!

[1] End-to-end encryption is currently in beta: blog post.

Synapse Installation

Synapse is the reference Python/Twisted Matrix homeserver implementation.

System requirements:

  • POSIX-compliant system (tested on Linux & OS X)
  • Python 3.5, 3.6, 3.7, or 2.7
  • At least 1GB of free RAM if you want to join large public rooms like

Installing from source

(Prebuilt packages are available for some platforms - see Platform-Specific Instructions.)

Synapse is written in Python but some of the libraries it uses are written in C. So before we can install Synapse itself we need a working C compiler and the header files for Python C extensions.

Installing prerequisites on Ubuntu or Debian:

sudo apt-get install build-essential python3-dev libffi-dev \
                     python-pip python-setuptools sqlite3 \
                     libssl-dev python-virtualenv libjpeg-dev libxslt1-dev

Installing prerequisites on ArchLinux:

sudo pacman -S base-devel python python-pip \
               python-setuptools python-virtualenv sqlite3

Installing prerequisites on CentOS 7 or Fedora 25:

sudo yum install libtiff-devel libjpeg-devel libzip-devel freetype-devel \
                 lcms2-devel libwebp-devel tcl-devel tk-devel redhat-rpm-config \
                 python-virtualenv libffi-devel openssl-devel
sudo yum groupinstall "Development Tools"

Installing prerequisites on Mac OS X:

xcode-select --install
sudo easy_install pip
sudo pip install virtualenv
brew install pkg-config libffi

Installing prerequisites on Raspbian:

sudo apt-get install build-essential python3-dev libffi-dev \
                     python-pip python-setuptools sqlite3 \
                     libssl-dev python-virtualenv libjpeg-dev

Installing prerequisites on openSUSE:

sudo zypper in -t pattern devel_basis
sudo zypper in python-pip python-setuptools sqlite3 python-virtualenv \
               python-devel libffi-devel libopenssl-devel libjpeg62-devel

Installing prerequisites on OpenBSD:

doas pkg_add python libffi py-pip py-setuptools sqlite3 py-virtualenv \
             libxslt jpeg

To install the Synapse homeserver run:

mkdir -p ~/synapse
virtualenv -p python3 ~/synapse/env
source ~/synapse/env/bin/activate
pip install --upgrade pip
pip install --upgrade setuptools
pip install matrix-synapse[all]

This installs Synapse, along with the libraries it uses, into a virtual environment under ~/synapse/env. Feel free to pick a different directory if you prefer.

This Synapse installation can then be later upgraded by using pip again with the update flag:

source ~/synapse/env/bin/activate
pip install -U matrix-synapse[all]

In case of problems, please see the Troubleshooting section below.

There is an offical synapse image available at which can be used with the docker-compose file available at contrib/docker. Further information on this including configuration options is available in the README on

Alternatively, Andreas Peters (previously Silvio Fricke) has contributed a Dockerfile to automate a synapse server in a single Docker image, at

Slavi Pantaleev has created an Ansible playbook, which installs the offical Docker image of Matrix Synapse along with many other Matrix-related services (Postgres database, riot-web, coturn, mxisd, SSL support, etc.). For more details, see

Configuring Synapse

Before you can start Synapse, you will need to generate a configuration file. To do this, run (in your virtualenv, as before):

cd ~/.synapse
python -m \
    --server-name \
    --config-path homeserver.yaml \
    --generate-config \

… substituting an appropriate value for --server-name. The server name determines the “domain” part of user-ids for users on your server: these will all be of the format It also determines how other matrix servers will reach yours for Federation. For a test configuration, set this to the hostname of your server. For a more production-ready setup, you will probably want to specify your domain ( rather than a matrix-specific hostname here (in the same way that your email address is probably rather than - but doing so may require more advanced setup - see Setting up Federation. Beware that the server name cannot be changed later.

This command will generate you a config file that you can then customise, but it will also generate a set of keys for you. These keys will allow your Home Server to identify itself to other Home Servers, so don’t lose or delete them. It would be wise to back them up somewhere safe. (If, for whatever reason, you do need to change your Home Server’s keys, you may find that other Home Servers have the old key cached. If you update the signing key, you should change the name of the key in the <server name>.signing.key file (the second word) to something different. See the spec for more information on key management.)

The default configuration exposes two HTTP ports: 8008 and 8448. Port 8008 is configured without TLS; it should be behind a reverse proxy for TLS/SSL termination on port 443 which in turn should be used for clients. Port 8448 is configured to use TLS with a self-signed certificate. If you would like to do initial test with a client without having to setup a reverse proxy, you can temporarly use another certificate. (Note that a self-signed certificate is fine for Federation). You can do so by changing tls_certificate_path, tls_private_key_path and tls_dh_params_path in homeserver.yaml; alternatively, you can use a reverse-proxy, but be sure to read Using a reverse proxy with Synapse when doing so.

Apart from port 8448 using TLS, both ports are the same in the default configuration.

Registering a user

You will need at least one user on your server in order to use a Matrix client. Users can be registered either via a Matrix client, or via a commandline script.

To get started, it is easiest to use the command line to register new users:

$ source ~/synapse/env/bin/activate
$ synctl start # if not already running
$ register_new_matrix_user -c homeserver.yaml https://localhost:8448
New user localpart: erikj
Confirm password:
Make admin [no]:

This process uses a setting registration_shared_secret in homeserver.yaml, which is shared between Synapse itself and the register_new_matrix_user script. It doesn’t matter what it is (a random value is generated by --generate-config), but it should be kept secret, as anyone with knowledge of it can register users on your server even if enable_registration is false.

Setting up a TURN server

For reliable VoIP calls to be routed via this homeserver, you MUST configure a TURN server. See docs/turn-howto.rst for details.

Running Synapse

To actually run your new homeserver, pick a working directory for Synapse to run (e.g. ~/synapse), and:

cd ~/synapse
source env/bin/activate
synctl start

Connecting to Synapse from a client

The easiest way to try out your new Synapse installation is by connecting to it from a web client. The easiest option is probably the one at You will need to specify a “Custom server” when you log on or register: set this to https://domain.tld if you setup a reverse proxy following the recommended setup, or https://localhost:8448 - remember to specify the port (:8448) if not :443 unless you changed the configuration. (Leave the identity server as the default - see Identity servers.)

If using port 8448 you will run into errors until you accept the self-signed certificate. You can easily do this by going to https://localhost:8448 directly with your browser and accept the presented certificate. You can then go back in your web client and proceed further.

If all goes well you should at least be able to log in, create a room, and start sending messages.

Registering a new user from a client

By default, registration of new users via Matrix clients is disabled. To enable it, specify enable_registration: true in homeserver.yaml. (It is then recommended to also set up CAPTCHA - see docs/CAPTCHA_SETUP.rst.)

Once enable_registration is set to true, it is possible to register a user via or other Matrix clients.

Your new user name will be formed partly from the server_name (see Configuring synapse), and partly from a localpart you specify when you create the account. Your name will take the form of:

(pronounced “at localpart on my dot domain dot name”).

As when logging in, you will need to specify a “Custom server”. Specify your desired localpart in the ‘User name’ box.

Security Note

Matrix serves raw user generated data in some APIs - specifically the content repository endpoints.

Whilst we have tried to mitigate against possible XSS attacks (e.g. we recommend running matrix homeservers on a dedicated domain name, to limit any malicious user generated content served to web browsers a matrix API from being able to attack webapps hosted on the same domain. This is particularly true of sharing a matrix webclient and server on the same domain.

See and for more details.

Platform-Specific Instructions


Matrix provides official Debian packages via apt from Note that these packages do not include a client - choose one from (or build your own with one of our SDKs :)


Synapse is in the Fedora repositories as matrix-synapse:

sudo dnf install matrix-synapse

Oleg Girko provides Fedora RPMs at


Synapse is in the OpenSUSE repositories as matrix-synapse:

sudo zypper install matrix-synapse

SUSE Linux Enterprise Server

Unofficial package are built for SLES 15 in the openSUSE:Backports:SLE-15 repository at


The quickest way to get up and running with ArchLinux is probably with the community package, which should pull in most of the necessary dependencies.

pip may be outdated (6.0.7-1 and needs to be upgraded to 6.0.8-1 ):

sudo pip install --upgrade pip

If you encounter an error with lib bcrypt causing an Wrong ELF Class: ELFCLASS32 (x64 Systems), you may need to reinstall py-bcrypt to correctly compile it under the right architecture. (This should not be needed if installing under virtualenv):

sudo pip uninstall py-bcrypt
sudo pip install py-bcrypt


Synapse can be installed via FreeBSD Ports or Packages contributed by Brendan Molloy from:

  • Ports: cd /usr/ports/net-im/py-matrix-synapse && make install clean
  • Packages: pkg install py27-matrix-synapse


There is currently no port for OpenBSD. Additionally, OpenBSD’s security settings require a slightly more difficult installation process.

  1. Create a new directory in /usr/local called _synapse. Also, create a new user called _synapse and set that directory as the new user’s home. This is required because, by default, OpenBSD only allows binaries which need write and execute permissions on the same memory space to be run from /usr/local.
  2. su to the new _synapse user and change to their home directory.
  3. Create a new virtualenv: virtualenv -p python2.7 ~/.synapse
  4. Source the virtualenv configuration located at /usr/local/_synapse/.synapse/bin/activate. This is done in ksh by using the . command, rather than bash’s source.
  5. Optionally, use pip to install lxml, which Synapse needs to parse webpages for their titles.
  6. Use pip to install this repository: pip install matrix-synapse
  7. Optionally, change _synapse’s shell to /bin/false to reduce the chance of a compromised Synapse server being used to take over your box.

After this, you may proceed with the rest of the install directions.

Windows Install

If you wish to run or develop Synapse on Windows, the Windows Subsystem For Linux provides a Linux environment on Windows 10 which is capable of using the Debian, Fedora, or source installation methods. More information about WSL can be found at for Windows 10 and for Windows Server.


Troubleshooting Installation

Synapse requires pip 8 or later, so if your OS provides too old a version you may need to manually upgrade it:

sudo pip install --upgrade pip

Installing may fail with Could not find any downloads that satisfy the requirement pymacaroons-pynacl (from matrix-synapse==0.12.0). You can fix this by manually upgrading pip and virtualenv:

sudo pip install --upgrade virtualenv

You can next rerun virtualenv -p python3 synapse to update the virtual env.

Installing may fail during installing virtualenv with InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see You can fix this by manually installing ndg-httpsclient:

pip install --upgrade ndg-httpsclient

Installing may fail with mock requires setuptools>=17.1. Aborting installation. You can fix this by upgrading setuptools:

pip install --upgrade setuptools

If pip crashes mid-installation for reason (e.g. lost terminal), pip may refuse to run until you remove the temporary installation directory it created. To reset the installation:

rm -rf /tmp/pip_install_matrix

pip seems to leak lots of memory during installation. For instance, a Linux host with 512MB of RAM may run out of memory whilst installing Twisted. If this happens, you will have to individually install the dependencies which are failing, e.g.:

pip install twisted

Running out of File Handles

If synapse runs out of filehandles, it typically fails badly - live-locking at 100% CPU, and/or failing to accept new TCP connections (blocking the connecting client). Matrix currently can legitimately use a lot of file handles, thanks to busy rooms like containing hundreds of participating servers. The first time a server talks in a room it will try to connect simultaneously to all participating servers, which could exhaust the available file descriptors between DNS queries & HTTPS sockets, especially if DNS is slow to respond. (We need to improve the routing algorithm used to be better than full mesh, but as of June 2017 this hasn’t happened yet).

If you hit this failure mode, we recommend increasing the maximum number of open file handles to be at least 4096 (assuming a default of 1024 or 256). This is typically done by editing /etc/security/limits.conf

Separately, Synapse may leak file handles if inbound HTTP requests get stuck during processing - e.g. blocked behind a lock or talking to a remote server etc. This is best diagnosed by matching up the ‘Received request’ and ‘Processed request’ log lines and looking for any ‘Processed request’ lines which take more than a few seconds to execute. Please let us know at if you see this failure mode so we can help debug it, however.

Upgrading an existing Synapse

The instructions for upgrading synapse are in UPGRADE.rst. Please check these instructions as upgrading may require extra steps for some versions of synapse.

Setting up Federation

Federation is the process by which users on different servers can participate in the same room. For this to work, those other servers must be able to contact yours to send messages.

As explained in Configuring synapse, the server_name in your homeserver.yaml file determines the way that other servers will reach yours. By default, they will treat it as a hostname and try to connect to port 8448. This is easy to set up and will work with the default configuration, provided you set the server_name to match your machine’s public DNS hostname.

For a more flexible configuration, you can set up a DNS SRV record. This allows you to run your server on a machine that might not have the same name as your domain name. For example, you might want to run your server at, but have your Matrix user-ids look like (A SRV record also allows you to change the port from the default 8448. However, if you are thinking of using a reverse-proxy on the federation port, which is not recommended, be sure to read Reverse-proxying the federation port first.)

To use a SRV record, first create your SRV record and publish it in DNS. This should have the format _matrix._tcp.<> <ttl> IN SRV 10 0 <port> <>. The DNS record should then look something like:

$ dig -t srv 3600    IN      SRV     10 0 8448

Note that the server hostname cannot be an alias (CNAME record): it has to point directly to the server hosting the synapse instance.

You can then configure your homeserver to use <> as the domain in its user-ids, by setting server_name:

python -m \
    --server-name <> \
    --config-path homeserver.yaml \
python -m --config-path homeserver.yaml

If you’ve already generated the config file, you need to edit the server_name in your homeserver.yaml file. If you’ve already started Synapse and a database has been created, you will have to recreate the database.

If all goes well, you should be able to connect to your server with a client, and then join a room via federation. (Try as a first step. “Matrix HQ“‘s sheer size and activity level tends to make even the largest boxes pause for thought.)


You can use the federation tester to check if your homeserver is all set:<your_server_name> If any of the attributes under “checks” is false, federation won’t work.

The typical failure mode with federation is that when you try to join a room, it is rejected with “401: Unauthorized”. Generally this means that other servers in the room couldn’t access yours. (Joining a room over federation is a complicated dance which requires connections in both directions).

So, things to check are:

  • If you are trying to use a reverse-proxy, read Reverse-proxying the federation port.
  • If you are not using a SRV record, check that your server_name (the part of your user-id after the :) matches your hostname, and that port 8448 on that hostname is reachable from outside your network.
  • If you are using a SRV record, check that it matches your server_name (it should be _matrix._tcp.<server_name>), and that the port and hostname it specifies are reachable from outside your network.

Running a Demo Federation of Synapses

If you want to get up and running quickly with a trio of homeservers in a private federation, there is a script in the demo directory. This is mainly useful just for development purposes. See demo/README.

Using PostgreSQL

As of Synapse 0.9, PostgreSQL is supported as an alternative to the SQLite database that Synapse has traditionally used for convenience and simplicity.

The advantages of Postgres include:

  • significant performance improvements due to the superior threading and caching model, smarter query optimiser
  • allowing the DB to be run on separate hardware
  • allowing basic active/backup high-availability with a “hot spare” synapse pointing at the same DB master, as well as enabling DB replication in synapse itself.

For information on how to install and use PostgreSQL, please see docs/postgres.rst.

Using a reverse proxy with Synapse

It is recommended to put a reverse proxy such as nginx, Apache, Caddy or HAProxy in front of Synapse. One advantage of doing so is that it means that you can expose the default https port (443) to Matrix clients without needing to run Synapse with root privileges.

The most important thing to know here is that Matrix clients and other Matrix servers do not necessarily need to connect to your server via the same port. Indeed, clients will use port 443 by default, whereas servers default to port 8448. Where these are different, we refer to the ‘client port’ and the ‘federation port’.

The next most important thing to know is that using a reverse-proxy on the federation port has a number of pitfalls. It is possible, but be sure to read Reverse-proxying the federation port.

The recommended setup is therefore to configure your reverse-proxy on port 443 to port 8008 of synapse for client connections, but to also directly expose port 8448 for server-server connections. All the Matrix endpoints begin /_matrix, so an example nginx configuration might look like:

server {
    listen 443 ssl;
    listen [::]:443 ssl;

    location /_matrix {
        proxy_pass http://localhost:8008;
        proxy_set_header X-Forwarded-For $remote_addr;

an example Caddy configuration might look like: {
  proxy /_matrix http://localhost:8008 {

and an example Apache configuration might look like:

<VirtualHost *:443>
    SSLEngine on

    <Location /_matrix>
        ProxyPass nocanon

You will also want to set bind_addresses: [''] and x_forwarded: true for port 8008 in homeserver.yaml to ensure that client IP addresses are recorded correctly.

Having done so, you can then use (instead of as the “Custom server” when Connecting to Synapse from a client.

Reverse-proxying the federation port

There are two issues to consider before using a reverse-proxy on the federation port:

  • Due to the way SSL certificates are managed in the Matrix federation protocol (see spec), Synapse needs to be configured with the path to the SSL certificate, even if you do not terminate SSL at Synapse.
  • Until v0.33.3, Synapse did not support SNI on the federation port (bug #1491). This bug is now fixed, but means that federating with older servers can be unreliable when using name-based virtual hosting.

Furthermore, a number of the normal reasons for using a reverse-proxy do not apply:

  • Other servers will connect on port 8448 by default, so there is no need to listen on port 443 (for federation, at least), which avoids the need for root privileges and virtual hosting.
  • A self-signed SSL certificate is fine for federation, so there is no need to automate renewals. (The certificate generated by --generate-config is valid for 10 years.)

If you want to set up a reverse-proxy on the federation port despite these caveats, you will need to do the following:

  • In homeserver.yaml, set tls_certificate_path to the path to the SSL certificate file used by your reverse-proxy, and set no_tls to True. (tls_private_key_path will be ignored if no_tls is True.)
  • In your reverse-proxy configuration:
    • If there are other virtual hosts on the same port, make sure that the default one uses the certificate configured above.
    • Forward /_matrix to Synapse.
  • If your reverse-proxy is not listening on port 8448, publish a SRV record to tell other servers how to find you. See Setting up Federation.

When updating the SSL certificate, just update the file pointed to by tls_certificate_path and then restart Synapse. (You may like to use a symbolic link to help make this process atomic.)

The most common mistake when setting up federation is not to tell Synapse about your SSL certificate. To check it, you can visit<your_server_name>. Unfortunately, there is no UI for this yet, but, you should see "MatchingTLSFingerprint": true. If not, check that Certificates[0].SHA256Fingerprint (the fingerprint of the certificate presented by your reverse-proxy) matches Keys.tls_fingerprints[0].sha256 (the fingerprint of the certificate Synapse is using).

Identity Servers

Identity servers have the job of mapping email addresses and other 3rd Party IDs (3PIDs) to Matrix user IDs, as well as verifying the ownership of 3PIDs before creating that mapping.

They are not where accounts or credentials are stored - these live on home servers. Identity Servers are just for mapping 3rd party IDs to matrix IDs.

This process is very security-sensitive, as there is obvious risk of spam if it is too easy to sign up for Matrix accounts or harvest 3PID data. In the longer term, we hope to create a decentralised system to manage it (matrix-doc #712), but in the meantime, the role of managing trusted identity in the Matrix ecosystem is farmed out to a cluster of known trusted ecosystem partners, who run ‘Matrix Identity Servers’ such as Sydent, whose role is purely to authenticate and track 3PID logins and publish end-user public keys.

You can host your own copy of Sydent, but this will prevent you reaching other users in the Matrix ecosystem via their email address, and prevent them finding you. We therefore recommend that you use one of the centralised identity servers at or for now.

To reiterate: the Identity server will only be used if you choose to associate an email address with your account, or send an invite to another user via their email address.

URL Previews

Synapse 0.15.0 introduces a new API for previewing URLs at /_matrix/media/r0/preview_url. This is disabled by default. To turn it on you must enable the url_preview_enabled: True config parameter and explicitly specify the IP ranges that Synapse is not allowed to spider for previewing in the url_preview_ip_range_blacklist configuration parameter. This is critical from a security perspective to stop arbitrary Matrix users spidering ‘internal’ URLs on your network. At the very least we recommend that your loopback and RFC1918 IP addresses are blacklisted.

This also requires the optional lxml and netaddr python dependencies to be installed. This in turn requires the libxml2 library to be available - on Debian/Ubuntu this means apt-get install libxml2-dev, or equivalent for your OS.

Password reset

If a user has registered an email address to their account using an identity server, they can request a password-reset token via clients such as Riot.

A manual password reset can be done via direct database access as follows.

First calculate the hash of the new password:

$ source ~/.synapse/bin/activate
$ ./scripts/hash_password
Confirm password:

Then update the users table in the database:

UPDATE users SET password_hash='$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
    WHERE name='';

Synapse Development

Before setting up a development environment for synapse, make sure you have the system dependencies (such as the python header files) installed - see Installing from source.

To check out a synapse for development, clone the git repo into a working directory of your choice:

git clone
cd synapse

Synapse has a number of external dependencies, that are easiest to install using pip and a virtualenv:

virtualenv -p python2.7 env
source env/bin/activate
python -m pip install -e .[all]

This will run a process of downloading and installing all the needed dependencies into a virtual env.

Once this is done, you may wish to run Synapse’s unit tests, to check that everything is installed as it should be:

python -m twisted.trial tests

This should end with a ‘PASSED’ result:

Ran 143 tests in 0.601s

PASSED (successes=143)

Running the Integration Tests

Synapse is accompanied by SyTest, a Matrix homeserver integration testing suite, which uses HTTP requests to access the API as a Matrix client would. It is able to run Synapse directly from the source tree, so installation of the server is not required.

Testing with SyTest is recommended for verifying that changes related to the Client-Server API are functioning correctly. See the installation instructions for details.

Building Internal API Documentation

Before building internal API documentation install sphinx and sphinxcontrib-napoleon:

pip install sphinx
pip install sphinxcontrib-napoleon

Building internal API documentation:

python build_sphinx

Help!! Synapse eats all my RAM!

Synapse’s architecture is quite RAM hungry currently - we deliberately cache a lot of recent room data and metadata in RAM in order to speed up common requests. We’ll improve this in future, but for now the easiest way to either reduce the RAM usage (at the risk of slowing things down) is to set the almost-undocumented SYNAPSE_CACHE_FACTOR environment variable. The default is 0.5, which can be decreased to reduce RAM usage in memory constrained enviroments, or increased if performance starts to degrade.

Using libjemalloc can also yield a significant improvement in overall amount, and especially in terms of giving back RAM to the OS. To use it, the library must simply be put in the LD_PRELOAD environment variable when launching Synapse. On Debian, this can be done by installing the libjemalloc1 package and adding this line to /etc/default/matrix-synapse:


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