=============
Server tuning
=============

Using cron to perform background jobs
-------------------------------------

See :doc:`../configuration_server/background_jobs_configuration` for a description and the
benefits.

Reducing system load
--------------------

High system load will slow down Nextcloud and might also lead to other unwanted
side effects. To reduce load you should first identify the source of the problem.
Tools such as htop, iotop, `netdata <https://my-netdata.io>`_ or
`glances <https://nicolargo.github.io/glances/>`_
will help to identify the process or the drive that slows down your system. First
you should make sure that you installed/assigned enough RAM. Swap usage should be
prevented by all means. If you run your database inside a VM, you should not
store it inside a VM image file. Better put it on a dedicated block device to
reduce latency due to multiple abstraction layers.

.. _caching:

Caching
-------

Caching improves performance by storing data, code, and other objects in memory.
Memory cache configuration for the Nextcloud server must be installed and configured.
See :doc:`../configuration_server/caching_configuration`.

Using MariaDB/MySQL instead of SQLite
-------------------------------------

MySQL or MariaDB are preferred because of the `performance limitations of
SQLite with highly concurrent applications
<https://www.sqlite.org/whentouse.html>`_, like Nextcloud.

See the section :doc:`../configuration_database/linux_database_configuration` for how to
configure Nextcloud for MySQL or MariaDB. If your installation is already running on
SQLite then it is possible to convert to MySQL or MariaDB using the steps provided
in :doc:`../configuration_database/db_conversion`.

For more details and help tuning your database, check `this article at MariaDB <https://mariadb.com/kb/en/optimization-and-tuning/>`_.

Using Redis-based transactional file locking
--------------------------------------------

File locking is enabled by default, using the database locking backend. This
places a significant load on your database. See the section
:doc:`../configuration_files/files_locking_transactional` for how to
configure Nextcloud to use Redis-based Transactional File Locking.

TLS / encryption app
--------------------

TLS (HTTPS) and file encryption/decryption can be offloaded to a processor's
AES-NI extension. This can both speed up these operations while lowering
processing overhead. This requires a processor with the `AES-NI instruction set
<https://wikipedia.org/wiki/AES_instruction_set>`_.

Here are some examples how to check if your CPU / environment supports the
AES-NI extension:

* For each CPU core present: ``grep flags /proc/cpuinfo`` or as a summary for
  all cores: ``grep -m 1 '^flags' /proc/cpuinfo`` If the result contains any
  ``aes``, the extension is present.

* Search eg. on the Intel web if the processor used supports the extension
  `Intel Processor Feature Filter
  <https://ark.intel.com/MySearch.aspx?AESTech=true>`_ You may set a filter by
  ``"AES New Instructions"`` to get a reduced result set.

* For versions of openssl >= 1.0.1, AES-NI does not work via an engine and
  will not show up in the ``openssl engine`` command. It is active by default
  on the supported hardware. You can check the openssl version via ``openssl
  version -a``

* If your processor supports AES-NI but it does not show up eg via grep or
  coreinfo, it is maybe disabled in the BIOS.

* If your environment runs virtualized, check the virtualization vendor for
  support.

Enable HTTP/2 for faster loading
--------------------------------

HTTP/2 has `huge speed improvements <https://www.troyhunt.com/i-wanna-go-fast-https-massive-speed-advantage/>`_ over HTTP with multiple request. Most `browsers already support HTTP/2 over TLS (HTTPS) <https://caniuse.com/#feat=http2>`_. Refer to your web server manual for guides on how to enable HTTP/2.

Tune PHP-FPM
------------

If you are using a default installation of PHP-FPM you might have noticed
excessive load times on the web interface or even sync issues. This is due
to the fact that each simultaneous request of an element is handled by a
separate PHP-FPM process. So even on a small installation you should allow
more processes to run in parallel to handle the requests.

`This link <https://spot13.com/pmcalculator/>`_ can help you calculate the good values for your system.

Enable PHP OPcache
------------------

The `OPcache <https://php.net/manual/en/intro.opcache.php>`_ improves the performance of PHP applications by caching precompiled bytecode. The default OPcache settings are usually sufficient for Nextcloud code to be fully cached. If any cache size limit is reached by more than 90%, the admin panel will show a related warning. Nextcloud strictly requires code comments to be preserved in opcode, which is the default. But in case PHP settings are changed on your system, you may need set the following:

.. code:: ini

  opcache.save_comments = 1

By default, cached scripts are revalidated on access to ensure that changes on disk take effect after at most ``2`` seconds. Since Nextcloud handles cache revalidation internally when required, the revalidation frequency can be reduced or completely disabled to enhance performance. Note, however, that it affects manual changes to scripts, including ``config.php``. To check for changes at most every ``60`` seconds, use the following setting:

.. code:: ini

  opcache.revalidate_freq = 60

To disable the revalidation completely:

.. code:: ini

  opcache.validate_timestamps = 0

Any change to ``config.php`` will then require either restarting PHP, manually clearing the cache, or invalidating this particular script.

For more details check out the `official documentation <https://php.net/manual/en/opcache.configuration.php>`_. To monitor OPcache usage, clear individual or all cache entries, `opcache-gui <https://github.com/amnuts/opcache-gui>`_ can be used.

Previews
--------

It is possible to speed up preview generation using an
external microservice: `Imaginary <https://github.com/h2non/imaginary>`_.

We strongly recommend running our custom docker image that is more up to date than the official image.
You can find the image at `docker.io/nextcloud/aio-imaginary:latest`.

To do so, you will need to deploy the service and make sure that it is
not accessible from outside of your servers. Then you can configure
Nextcloud to use Imaginary by editing your `config.php`:

.. code:: php

    <?php
    'enabledPreviewProviders' => [
        'OC\Preview\MP3',
        'OC\Preview\TXT',
        'OC\Preview\MarkDown',
        'OC\Preview\OpenDocument',
        'OC\Preview\Krita',
        'OC\Preview\Imaginary',
    ],
    'preview_imaginary_url' => 'http://<url of imaginary>',

.. warning::

   Make sure to start Imaginary with the `-return-size` command line parameter. Otherwise, there will be a minor performance impact. The flag requires a recent version of Imaginary (newer than v1.2.4) and is by default added to the `aio-imaginary` container.
   Also make sure to add the capability `SYS_NICE` via `--cap-add=sys_nice` or `cap_add: - SYS_NICE` as it is required by imaginary to generate HEIC previews.

.. note::

    For large instance, you should follow `Imaginary's scability recommandation <https://github.com/h2non/imaginary#scalability>`_.
