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# 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 so they don’t need to be re-compiled every time they are called. These compiled PHP scripts are stored in-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.

## Supported Caching Backends

The caching backends supported by ownCloud are:

- APCu: This is a local cache for systems running PHP 5.6 and up. APCu 4.0.6 and up is required. Alternatively you can use the Zend OPCache. However, it is not a data cache, only an opcode cache.
- Redis: This is a distributed cache for multi-server ownCloud installations. Version 2.2.6 or higher of the PHP Redis extension is required.
- Memcached: This is a distributed cache for multi-server ownCloud installations.

Note

You may use both a local and a distributed cache. The recommended ownCloud caches are APCu and Redis.

Note

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 `config.php` (See Config.php Parameters) to select a different location.

## Cache Types

### APCu

PHP 5.6 and up include the Zend OPcache in core, and on most Linux distributions it is enabled by default. However, it does not bundle a data cache. Given that, we recommend that you use APCu instead. APCu is a data cache and is available in most Linux distributions.

#### Installing APCu

    # On RedHat/CentOS/Fedora systems running PHP 5.6
    yum install rh-php56-php-devel
    pecl install apcu

    # On RedHat/CentOS/Fedora systems running PHP 7.0
    yum install rh-php70-php-devel
    pecl install apcu

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

Note

On Ubuntu 14.04 LTS, the APCu version is 4.0.2. This is too old to use with ownCloud, which requires ownCloud 4.0.6+. You can install 4.0.7 from Ubuntu backports with the following command:

    apt-get install php5-apcu/trusty-backports

After APCu’s installed, enable the extension by creating a configuration file for it, using the following commands.

    cat << EOF > /etc/opt/rh/rh-php70/php.d/20-apcu.ini
    ; APCu php extension
    extension=apcu.so
    EOF

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

### Redis

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 Redis PHP module must be at least version 2.2.6 or higher. If you are running a Linux distribution that does not package the supported versions of this module — or does not package Redis at all — see Installing Redis on other distributions.

Note

Debian Jessie users, please see this GitHub discussion if you have problems with LDAP authentication when using Redis.

#### Installing Redis on Debian-based Distributions

On Debian/Ubuntu/Mint run the following command:

    apt-get install redis-server php5-redis

If you have Ubuntu 16.04 or higher:

    apt install redis-server php-redis

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

Note

If you’re running ownCloud on Ubuntu 14.04, which does not package the required version of `php5-redis`, then work through this guide on Tech and Me to see how to install and configure it.

#### Installing Redis on RedHat, CentOS, and Fedora

On RedHat, CentOS, and Fedora run the following commands to install Redis:

    yum install rh-php70-php-devel rh-redis32-redis
    pecl install redis

Unlike on Debian-based distributions, Redis will not start automatically on RedHat, Centos, and Fedora. Given that, you must use your service manager to both start Redis, and to launch it at boot time as a daemon. To do so, run the following commands:

    systemctl start rh-redis32-redis
    systemctl enable rh-redis32-redis

You can verify that the Redis daemon is running using either of the following two commands:

    ps ax | grep redis
    netstat -tlnp | grep redis

When it’s running, enable the Redis extension by creating a configuration file for it, using the following commands.

    cat << EOF > /etc/opt/rh/rh-php70/php.d/20-redis.ini
    ; Redis php extension
    extension=redis.so
    EOF

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.

#### Installing Redis on other distributions

These instructions are adaptable for any distribution that does not package the supported version, or that does not package Redis at all, such as SUSE Linux Enterprise Server and RedHat Enterprise Linux.

Note

The Redis PHP module must be at least version 2.2.6.

##### On Debian/Mint/Ubuntu

Use `apt-cache` to see the available `php5-redis` version, or the version of your installed package:

    apt-cache policy php5-redis

##### On CentOS and Fedora

The `yum` command shows available and installed version information:

    yum search php-pecl-redis

#### 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>
    FLUSHDB

`<dbIndex>` is the number of Redis database where the cache is stored. It is zero by default at ownCloud. To check what yours is currently set to, check the `dbindex` value in `config/config.php`. Here’s an example of what to look for:

    'redis' => [
        'host' => 'localhost',  // Can also be a unix domain socket => '/tmp/redis.sock'
        'port' => 6379,
        'timeout' => 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.
    ],

##### Further Reading

- https://redis.io/commands/select
- https://redis.io/commands/flushdb

### Memcached

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.

Note

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 Debian/Ubuntu/Mint

On Debian/Ubuntu/Mint run the following command:

    apt-get install memcached php5-memcached

Note

The installer will automatically start `memcached` and configure it to launch at startup.

##### On RedHat/CentOS/Fedora

On RedHat/CentOS/Fedora run the following command:

    yum install memcached php-pecl-memcache

It will not start Memcached automatically after the installation or on subsequent reboots as a daemon, so you must do so yourself . To do so, run the following command:

    systemctl start memcached
    systemctl enable memcached

You can verify that the Memcached daemon is running using one of the following commands:

    ps ax | grep memcached
    netstat -tlnp | grep memcached

With the extension installed, you now need to configure it, by creating a configuration file for it. You can do so using the command below, substituting `FILE_PATH` with one from the list below the command.

    cat << EOF > FILE_PATH
    ; Memcached PHP extension
    extension=memcached.so
    EOF

#### Configuration File Paths

PHP Version | Filename
--- | ---
5.6 | `/etc/opt/rh/rh-php56/php.d/25-memcached.ini`
7.0 | `/etc/opt/rh/rh-php70/php.d/25-memcached.ini`

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 login, run the flush_all command, and logout:

    telnet localhost 11211
    flush_all
    quit

For more information see:

- https://github.com/memcached/memcached/wiki/Commands#flushall

## 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 Config.php Parameters for an overview of all possible config parameters. After installing and enabling your chosen memory cache, verify that it is active by running PHP Version and Information.

### 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

This example `config.php` configuration uses Redis for the local server cache:

     'memcache.local' => '\OC\Memcache\Redis',
     'redis' => [
         'host' => 'localhost',
         'port' => 6379,
     ],
    'memcache.locking' => '\OC\Memcache\Redis', // Add this for best performance

If you want to connect to Redis configured to listen on an Unix socket, which is recommended if Redis is running on the same system as ownCloud, use this example configuration:

    'memcache.local' => '\OC\Memcache\Redis',
    'redis' => [
         'host' => '/var/run/redis/redis.sock',
         'port' => 0,
    ],

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

### 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],
         ['server1.example.com', 11211],
         ['server2.example.com', 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' => '12.34.56.78',  // IP address example
        'port' => 6379,
    ],

### Configuring Transactional File Locking

Transactional File Locking prevents simultaneous file saving. To use it, you have to enable 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' => 0.0,
         'password' => '', // Optional, if not defined no password will be used.
     ],

Note

For enhanced security it is recommended to configure Redis to require a password. See http://redis.io/topics/security for more information.

## Caching Exceptions

If ownCloud is configured to use either Memcached or Redis as a memory cache, please be aware that 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

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