Memory Caching


You can significantly improve ownCloud server performance by using memory caching. This is the process of storing frequently requested objects in memory for faster retrieval later. There are two types of memory caching available:

A PHP opcode Cache (OPcache)

An opcode cache stores compiled PHP scripts (opcodes) so they don’t need to be parsed and compiled every time they are called. These compiled PHP scripts are stored in shared memory on the server on which they’re compiled.

A Data Cache

A data cache stores copies of data, templates, and other types of information-based files. Depending on the cache implementation, it can be either local or specific to one server or distributed across multiple servers. This cache type is ideal when you have a scale-out installation.

In addition, we suggest to use External Transactional File Locking which reduces load on the database significantly.

Supported Caching Backends

The caching backends supported by ownCloud are:

  • Opcache
    This is an opcode cache only and does not cache any data. Opcache is bundled with PHP from version 5.5.0 and later.

  • APCu
    This is a data cache only and does not cache any opcode. APCu 4.0.6 and up is required.

  • Redis
    This is an in-memory data structure store (cache) for single and multi-server ownCloud installations, which provides file locking and can be set up in local or distributed environments. Consider Redis younger, richer in features and more configurable than memcached. At least version 2.2.6 or higher of the PHP Redis extension is required.

  • Memcached
    This is a distributed cache for multi-server ownCloud installations and has no file locking capabilities.

See the following page to learn more about the Redis vs. Memcached – 2021 Comparison.

You may use both a local and a distributed cache. The recommended ownCloud caches are APCu and Redis. If you do not install and enable a local memory cache you will see a warning on your ownCloud admin page. If you enable only a distributed cache in your config.php (memcache.distributed) and not a local cache (memcache.local) you will still see the cache warning.

Cache Directory Location

The cache directory defaults to data/$user/cache where $user is the current user. You may use the 'cache_path' directive in your configuration for different locations. For details see the Define the location of the cache folder description.

Cache Types


Opcache should be enabled by default in your php installation. To check it, run the following command:

php -r 'phpinfo();' | grep opcache.enable


The easiest cache to use is APCu, because it is a data cache, very fast and nothing needs to be configured. APCu can not be used when needed to run on an external server.

Installing APCu

# On Ubuntu/Debian/Mint systems
sudo apt install php-apcu

With that done, assuming that you don’t encounter any errors, restart Apache and the extension is ready to use.


Redis is an excellent modern memory cache to use for both distributed caching and as a local cache for transactional file locking, because it guarantees that cached objects are available for as long as they are needed.

The performance of Redis when used with a socket connection is close to the performance of APCu.

The Redis PHP module must be at least version 2.2.6 or higher.
The default shipped Redis version and the php-redis extension for Ubuntu 20.04 is 5.x. With Redis version 6, a new authentication mechanism has been introduced named ACL (Access Control Lists). ownCloud does not currently support Redis ACL´s, but does support the password protection available with current Redis versions.

Installing Redis

If you have Ubuntu 16.04 or higher:

sudo apt install redis-server php-redis

The installer will automatically launch Redis and configure it to launch at startup.

After that, assuming that you don’t encounter any errors, restart Apache and the extension is ready to use.

Additional notes for Redis vs. APCu on Memory Caching

APCu is faster at local caching than Redis. If you have enough memory, use APCu for memory caching and Redis for file locking. If you are low on memory, use Redis for both.

Clearing the Redis Cache

The Redis cache can be flushed from the command-line using the redis-cli tool, as in the following example:

sudo redis-cli
SELECT <dbIndex>

<dbIndex> is the number of the Redis database where the cache is stored. It is zero by default at ownCloud. To check what yours is currently set to for ownCloud, check the dbindex value in config/config.php. To change it, see the Memory caching backend configuration

Out of the box, every Redis instance supports 16 databases so <dbIndex> has to be set between 0 and 15.

Please read more about the instructions for the select and flushdb command.


Memcached is a reliable old-timer for shared caching on distributed servers. It performs well with ownCloud with one exception: it is not suitable to use with Transactional File Locking. This is because it does not store locks, and data can disappear from the cache at any time. Given that, Redis is the best memory cache to use.

Be sure to install the memcached PHP module, and not memcache, as in the following examples. ownCloud supports only the memcached PHP module.

Installing Memcached

On Ubuntu/Debian/Mint

On Ubuntu/Debian/Mint run the following command:

sudo apt-get install memcached php-memcached
The installer will automatically start memcached and configure it to launch at startup.

Configuration File Paths

PHP Version Filename



After that, assuming that you don’t encounter any errors:

  1. Restart your Web server

  2. Add the appropriate entries to config.php (which you can find an example of below)

  3. Refresh your ownCloud admin page

Clearing the Memcached Cache

The Memcached cache can be flushed from the command line, using a range of common Linux/Unix tools including netcat and telnet. The following example uses telnet to log in, run the flush_all command, and log out:

telnet localhost 11211

Configuring Memory Caching

Memory caches must be explicitly configured in ownCloud by:

  1. Installing and enabling your desired cache (whether that be the PHP extension and/or the caching server).

  2. Adding the appropriate entry to ownCloud’s config.php.

See the Memory caching backend configuration for an overview of all possible config parameters, as the examples below only show basic configuration settings. After installing and enabling your chosen memory cache, verify that it is active by viewing the PHP configuration details.

Opcache Configuration

Opcache should already be configured with PHP 7, see the opcache documentation for details.

APCu Configuration

To use APCu, add this line to config.php:

'memcache.local' => '\OC\Memcache\APCu',

With that done, refresh your ownCloud admin page, and the cache warning should disappear.

Redis Configuration

Redis is very configurable; consult the Redis documentation to learn more.

Regardless of whether you have setup Redis to use TCP or a Unix socket, we recommend adding the following for best performance. This enables External Transactional File Locking based on Redis:

'filelocking.enabled' => true,
'memcache.locking' => '\OC\Memcache\Redis',

Redis Configuration Using TCP

The following example config.php configuration connects to a Redis cache via TCP:

'memcache.local' => '\OC\Memcache\Redis',
'redis' => [
    'host' => 'localhost',       // For a Unix domain socket, use '/var/run/redis/redis.sock'
    'port' => 6379,  // Set to 0 when using a Unix socket
    'timeout' => 0,              // Optional, keep connection open forever
    'password' => '',            // Optional, if not defined no password will be used.
    'dbindex' => 0,              // Optional, if undefined SELECT will not run and will
                                 // use Redis Server's default DB Index.

Redis Configuration Using Unix Sockets

If Redis is running on the same server as ownCloud, it is recommended to configure it to use Unix sockets. Then, configure ownCloud to communicate with Redis as in the following example.

# Change the host value, based on the socket's location in your distribution
'memcache.local' => '\OC\Memcache\Redis',
'redis' => [
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'password' => '',            // Optional, if not defined no password will be used.
    'dbindex' => 0,              // Optional, if undefined SELECT will not run and will
                                 // use Redis Server's default DB Index.

If setting up Redis to be accessed via a Unix socket from a webserver user, then consider the following:

  1. Make the webserver user www-data member of the group redis in /etc/group, e.g., redis:x:110:www-data

  2. In your Redis configuration (/etc/redis/redis.conf) set unixsocketperm to 770

To see a benchmark comparison, run:

sudo redis-benchmark -q -n 100000
sudo redis-benchmark -s /var/run/redis/redis-server.sock -q -n 100000

In the following table, you will see an example gain of about +20% when using sockets compared to TCP on localhost. The values can differ in your environment. Please do a local check.

Test TCP (requests/s) Socket (requests/s) Gain (%)





































































MSET (10 keys)




Memcached Configuration

This example uses APCu for the local cache, Memcached as the distributed memory cache, and lists all the servers in the shared cache pool with their port numbers:

'memcache.local' => '\OC\Memcache\APCu',
'memcache.distributed' => '\OC\Memcache\Memcached',
'memcached_servers' => [
     ['localhost', 11211],
     ['', 11211],
     ['', 11211],

Configuration Recommendations Based on Type of Deployment

Small/Private Home Server

// Only use APCu
'memcache.local' => '\OC\Memcache\APCu',

Small Organization, Single-server Setup

Use APCu for local caching, Redis for file locking

'memcache.local' => '\OC\Memcache\APCu',
'memcache.locking' => '\OC\Memcache\Redis',
'redis' => [
    'host' => 'localhost',
    'port' => 6379,

Large Organization, Clustered Setup

Use Redis for everything except a local memory cache. Use the server’s IP address or hostname so that it is accessible to other hosts:

'memcache.distributed' => '\OC\Memcache\Redis',
'memcache.locking' => '\OC\Memcache\Redis',
'memcache.local' => '\OC\Memcache\APCu',
'redis' => [
    'host' => 'server1',      // hostname example
    'host' => '',  // IP address example
    'port' => 6379,

Configure Transactional File Locking

Transactional File Locking prevents simultaneous file saving. It is enabled by default and uses the database to store the locking data. This places a significant load on your database. It is recommended to use a cache backend instead. You have to configure it in config.php as in the following example, which uses Redis as the cache backend:

'filelocking.enabled' => true,
'memcache.locking' => '\OC\Memcache\Redis',
'redis' => [
     'host' => 'localhost',
     'port' => 6379,
     'timeout' => 0,
     'password' => '',     // Optional, if not defined no password will be used.
For enhanced security, it is recommended to configure Redis to require a password. See for more information.

Caching Exceptions

If ownCloud is configured to use either Memcached or Redis as a memory cache, you may encounter issues with functionality. When these occur, it is usually a result of PHP being incorrectly configured or the relevant PHP extension not being available.

In the table below, you can see all of the known reasons for reduced or broken functionality related to caching.

Setup/Configuration Result

If file locking is enabled, but the locking cache class is missing, then an exception will appear in the web UI

The application will not be usable

If file locking is enabled and the locking cache is configured, but the PHP module missing.

There will be a white page/exception in web UI. It will be a full page issue, and the application will not be usable

All enabled, but the Redis server is not running

The application will be usable. But any file operation will return a "500 Redis went away" exception

If Memcache is configured for local and distributed, but the class is missing

There will be a white page and an exception written to the logs, This is because autoloading needs the missing class. So there is no way to show a page