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| title | parent | has_toc | nav_order | permalink |
|---|---|---|---|---|
| Optimise your installation | Installation | true | 11 | /installation/start/optimisation |
Optimise your installation
Now that you have Dendrite running, the following tweaks will improve the reliability and performance of your installation.
PostgreSQL connection limit
A PostgreSQL database engine is configured to allow only a certain number of connections.
This is typically controlled by the max_connections and superuser_reserved_connections
configuration items in postgresql.conf. Once these limits are violated, PostgreSQL will
immediately stop accepting new connections until some of the existing connections are closed.
This is a common source of misconfiguration and requires particular care.
If your PostgreSQL max_connections is set to 100 and superuser_reserved_connections is
set to 3 then you have an effective connection limit of 97 database connections. It is
therefore important to ensure that Dendrite doesn't violate that limit, otherwise database
queries will unexpectedly fail and this will cause problems both within Dendrite and for users.
If you are also running other software that uses the same PostgreSQL database engine, then you must also take into account that some connections will be already used by your other software and therefore will not be available to Dendrite. Check the configuration of any other software using the same database engine for their configured connection limits and adjust your calculations accordingly.
Dendrite has a max_open_conns configuration item in each database block to control how many
connections it will open to the database.
If you are using the global database pool then you only need to configure the
max_open_conns setting once in the global section.
If you are defining a database config per component then you will need to ensure that
the sum total of all configured max_open_conns to a given database server do not exceed
the connection limit. If you configure a total that adds up to more connections than are available
then this will cause database queries to fail.
You may wish to raise the max_connections limit on your PostgreSQL server to accommodate
additional connections, in which case you should also update the max_open_conns in your
Dendrite configuration accordingly. However be aware that this is only advisable on particularly
powerful servers that can handle the concurrent load of additional queries running at one time.
File descriptor limit
Most platforms have a limit on how many file descriptors a single process can open. All connections made by Dendrite consume file descriptors — this includes database connections and network requests to remote homeservers. When participating in large federated rooms where Dendrite must talk to many remote servers, it is often very easy to exhaust default limits which are quite low.
We currently recommend setting the file descriptor limit to 65535 to avoid such issues. Dendrite will log immediately after startup if the file descriptor limit is too low:
level=warning msg="IMPORTANT: Process file descriptor limit is currently 1024, it is recommended to raise the limit for Dendrite to at least 65535 to avoid issues"
UNIX systems have two limits: a hard limit and a soft limit. You can view the soft limit
by running ulimit -Sn and the hard limit with ulimit -Hn:
$ ulimit -Hn
1048576
$ ulimit -Sn
1024
Increase the soft limit before starting Dendrite:
ulimit -Sn 65535
The log line at startup should no longer appear if the limit is sufficient.
If you are running under a systemd service, you can instead add LimitNOFILE=65535 option
to the [Service] section of your service unit file.
DNS caching
Dendrite has a built-in DNS cache which significantly reduces the load that Dendrite will place on your DNS resolver. This may also speed up outbound federation.
Consider enabling the DNS cache by modifying the global section of your configuration file:
dns_cache:
enabled: true
cache_size: 4096
cache_lifetime: 600s
Time synchronisation
Matrix relies heavily on TLS which requires the system time to be correct. If the clock drifts then you may find that federation no works reliably (or at all) and clients may struggle to connect to your Dendrite server.
Ensure that the time is synchronised on your system by enabling NTP sync.