Memcached Slab Statistics in C# (Detailed Guide w/ Code Examples)

Use Case(s)

The "stats slabs" command in Memcached is used to retrieve a detailed report of slab statistics. In the context of C#, these stats can be useful to:

1. Monitor and troubleshoot running Memcached instances.
2. Analyze memory usage patterns by understanding how data gets allocated to different slabs.
3. Identify the need for changing slab settings based on collected metrics.

Code Examples

We will use EnyimMemcached, a popular C# client for Memcached.

1. Connect to Memcached and Retrieve Slab Statistics

using Enyim.Caching;
using Enyim.Caching.Memcached;
...

// Create a new MemcachedClient with your configuration
MemcachedClient client = new MemcachedClient();

// Get raw stats
var rawStats = client.Stats();

// Loop through each server's stats
foreach (var serverStats in rawStats)
{
    var serverEndPoint = serverStats.Key;
    var serverSlabStats = serverStats.Value;

    Console.WriteLine($"Server: {serverEndPoint}");

    // Loop through each slab's stats
    foreach (var slabStat in serverSlabStats)
    {
        Console.WriteLine($"\tSlab: {slabStat.Key}");

        // Loop through each stat in the slab
        foreach (var stat in slabStat.Value)
        {
            Console.WriteLine($"\t\t{stat.Key}: {stat.Value}");
        }
    }
}

This code connects to a Memcached instance and retrieves the 'stats slabs' info across all servers. It then iterates over the results, printing out the server name, the slab IDs, and their respective stats.

Best Practices

1. Avoid Frequent Fetching: Although fetching slab statistics can provide valuable insights, avoid doing it frequently as it may impact the performance of your Memcached instance.

2. Use in Non-Production Environment: It's best to use these commands in a testing or development environment. Running such commands in production could potentially slow down your application.

Common Mistakes

1. Misinterpreting Slab Stats: Remember that slabs are not equivalent to keys. They are rather chunks of memory where values are stored. Therefore, a single slab can hold multiple items.

FAQs

1. What does 'used_chunks' mean in slab stats?

• 'used_chunks' represents the number of memory chunks allocated to an item and currently in use within a particular slab class.

2. How do I know if my Memcached configuration needs adjustment based on slab stats?

• If you're consistently seeing a high number of evictions in certain slab classes along with high memory usage, you may need to adjust your Memcached configuration.