Memcached

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  1. Memcached Server Configuration for MediaWiki

This article details configuring and utilizing Memcached to improve the performance of your MediaWiki installation. Memcached is a high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load. For a busy MediaWiki site, Memcached can dramatically reduce response times and improve overall scalability.

What is Memcached?

Memcached operates by storing frequently accessed data in RAM, allowing for quicker retrieval than repeatedly querying the database. It's particularly effective for caching data that's expensive to generate, such as the results of complex database queries used for page rendering. MediaWiki, by default, relies heavily on database queries. Caching frequently accessed parts of pages significantly reduces the load on the database server, leading to faster page loads for users. While PHP is commonly used with Memcached, other languages can also interface with it.

Installation

The installation process varies depending on your operating system. Here's a general overview. These instructions assume you have root or administrator privileges.

Linux (Debian/Ubuntu)

Open a terminal and execute the following commands:

```bash sudo apt update sudo apt install memcached php-memcached ```

Linux (CentOS/RHEL)

Open a terminal and execute the following commands:

```bash sudo yum install memcached php-pecl-memcached ```

Windows

Installation on Windows typically involves downloading a pre-compiled binary of Memcached and a PHP extension (usually a DLL file). Refer to the official Memcached documentation for detailed instructions: [1](http://memcached.org/). You will also need to configure your `php.ini` file to load the `php_memcached.dll` extension.

Configuration

After installation, you need to configure both Memcached itself and MediaWiki to utilize it.

Memcached Configuration

The Memcached configuration file is typically located at `/etc/memcached.conf` (Linux) or in the Memcached installation directory (Windows). Here are some key settings:

Parameter Description Default Value
`-m` Maximum amount of memory to use in MB. 64
`-p` Port to listen on. 11211
`-l` Interface address to listen on. 127.0.0.1
`-u` User to run as. root
`-t` Number of threads. 4

Adjust these values based on your server's resources and expected load. Increasing the memory allocation (`-m`) is usually the most effective way to improve performance.

MediaWiki Configuration

Edit your `LocalSettings.php` file. Add the following lines:

```php $wgMemCachedLocalServers = array( 

   '127.0.0.1:11211' // Replace with your Memcached server address and port

);

$wgCacheDirector = true; ```

`$wgMemCachedLocalServers` defines the Memcached servers that MediaWiki will use. You can specify multiple servers for redundancy and scalability. `$wgCacheDirector = true;` enables the caching director, which manages the caching process.

Advanced Configuration and Monitoring

For larger deployments, consider these advanced configurations:

Multiple Memcached Servers

For increased redundancy and capacity, you can configure MediaWiki to use multiple Memcached servers. Simply add more entries to the `$wgMemCachedLocalServers` array in `LocalSettings.php`.

```php $wgMemCachedLocalServers = array( 

   '127.0.0.1:11211',
   '192.168.1.10:11211',
   '192.168.1.11:11211'

); ```

Statistics and Monitoring

Memcached provides a simple text-based interface for monitoring its performance. You can use the `telnet` command to connect to the Memcached server and retrieve statistics.

```bash telnet 127.0.0.1 11211 ```

Once connected, type `stats` and press Enter to view detailed statistics. Tools like Nagios, Zabbix, or Memcached monitoring web interfaces can provide more comprehensive monitoring.

Caching Levels

MediaWiki uses different caching levels. Memcached primarily impacts the following:

  • **Parser Cache:** Caches the output of the parser, reducing the need to re-parse pages frequently.
  • **Query Cache:** Caches the results of database queries.
  • **Object Cache:** Caches various PHP objects used by MediaWiki.

Troubleshooting

Here are some common issues and their solutions:

Problem Solution
Memcached not connecting Verify Memcached is running. Check the server address and port in `LocalSettings.php`. Ensure firewalls aren't blocking the connection.
Pages not caching Check the `$wgCacheDirector` setting in `LocalSettings.php`. Verify the PHP Memcached extension is loaded. Clear the MediaWiki cache (using Special:Purge or by manually deleting cache files).
High memory usage Increase the memory allocation (`-m`) in the Memcached configuration file. Monitor the cache hit rate to determine if caching is effective.

Security Considerations

  • **Access Control:** By default, Memcached listens on localhost (127.0.0.1). If you need to access it from other servers, ensure you configure appropriate access control measures to prevent unauthorized access. Consider using a firewall.
  • **Data Sensitivity:** Memcached stores data in plain text in RAM. Do *not* cache sensitive information, such as passwords, in Memcached.
  • **Regular Monitoring:** Monitor Memcached's performance and resource usage to identify potential issues and ensure it's operating efficiently.

See Also


Intel-Based Server Configurations

Configuration Specifications Benchmark
Core i7-6700K/7700 Server 64 GB DDR4, NVMe SSD 2 x 512 GB CPU Benchmark: 8046
Core i7-8700 Server 64 GB DDR4, NVMe SSD 2x1 TB CPU Benchmark: 13124
Core i9-9900K Server 128 GB DDR4, NVMe SSD 2 x 1 TB CPU Benchmark: 49969
Core i9-13900 Server (64GB) 64 GB RAM, 2x2 TB NVMe SSD
Core i9-13900 Server (128GB) 128 GB RAM, 2x2 TB NVMe SSD
Core i5-13500 Server (64GB) 64 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Server (128GB) 128 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Workstation 64 GB DDR5 RAM, 2 NVMe SSD, NVIDIA RTX 4000

AMD-Based Server Configurations

Configuration Specifications Benchmark
Ryzen 5 3600 Server 64 GB RAM, 2x480 GB NVMe CPU Benchmark: 17849
Ryzen 7 7700 Server 64 GB DDR5 RAM, 2x1 TB NVMe CPU Benchmark: 35224
Ryzen 9 5950X Server 128 GB RAM, 2x4 TB NVMe CPU Benchmark: 46045
Ryzen 9 7950X Server 128 GB DDR5 ECC, 2x2 TB NVMe CPU Benchmark: 63561
EPYC 7502P Server (128GB/1TB) 128 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/2TB) 128 GB RAM, 2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/4TB) 128 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/1TB) 256 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/4TB) 256 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 9454P Server 256 GB RAM, 2x2 TB NVMe

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⚠️ *Note: All benchmark scores are approximate and may vary based on configuration. Server availability subject to stock.* ⚠️

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