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How to Handle Cache Overflow Scenarios in ASP.NET?

Are you tired of your ASP.NET caching system crashing due to overflow issues? Do you want to learn how to handle cache overflow scenarios like a pro? Well, look no further, because I've got some tips and tricks for you to ensure your caching system runs smoothly and efficiently. To ensure optimal performance and prevent cache overflow scenarios in ASP.NET, it is important to understand the underlying concepts and techniques for handling cache overflow effectively. In this article, we will explore the causes and effects of cache overflow and provide tips and best practices on How to Handle Cache Overflow Scenarios in ASP.NET?


So, let us first understand what Cache Overflow is and why they problematic for ASP.NET Caching?.


What is Cache Overflow?

Cache overflow in ASP.NET is a situation where the cache grows too large and consumes too much memory, causing performance issues or cache eviction. Cache eviction is when the cache removes some items to free up space for new items. This can result in losing some cached data that might be still useful or expensive to regenerate.


They are problematic for ASP.NET Caching because ASP.NET Core does not limit cache size based on memory pressure. It’s up to the developer to limit cache size by using expirations, SetSize, Size, and SizeLimit options. Alternatively, the developer can use a distributed cache to store data in memory when the app is hosted in a cloud or server farm. A distributed cache can support higher scale-out than an in-memory cache and avoid cache consistency problems


Common causes of cache overflow in ASP.NET caching are:

  • Inserting external input into the cache without limiting its size or expiration.

  • Not using SetSize, Size, and SizeLimit options to limit cache size.

  • Not using a distributed cache when the app is hosted in a cloud or server farm.

  • Not using cache dependencies to invalidate cache entries when the source data changes.

Common symptoms of cache overflow in ASP.NET caching are:

  • Performance degradation or application failure due to memory pressure.

  • Data inconsistency or stale data due to multiple cache instances not being synchronized.

  • Cache stampede or thundering herd problems due to too many requests trying to repopulate the same cache entry at the same time.

  • Cache misses and increase the workload on the source data due to low memory, expiration or dependency changes.


How to Handle Cache Overflow Scenarios in ASP.NET?

To handle cache overflow scenarios in ASP.NET, You need to use some techniques to limit the cache size, control the cache expiration, and monitor the cache usage. Some of these techniques are:


Technique 1. Setting Cache Size Limits and Priorities

One technique to handle cache overflow scenarios in ASP.NET Caching is to use cache size limits and priorities. This technique allows you to specify how much memory the cache can use and how important each cached item is. Here are some steps to implement this technique:


STEP 1: If you are using System.Web.Caching.Cache, you can use the CacheItemPriority enumeration to assign relative priorities to cached items. The cache automatically removes the lowest priority items when it needs to free memory. For example, add an item to the cache with a high priority:

Cache.Insert("key", value, null, Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration, CacheItemPriority.High, null);

STEP 2: If you are using System.Runtime.Caching.MemoryCache or IMemoryCache, you can use the MemoryCacheEntryOptions class to configure various aspects of cache entries, such as expiration, priority, size, and dependencies. For example, add an item to the cache with a high priority and a size of 1 unit:

var options = new MemoryCacheEntryOptions()
    .SetPriority(CacheItemPriority.High)
    .SetSize(1);

cache.Set("key", value, options);

STEP 3: To limit the cache size, you need to specify the SizeLimit property of the cache instance. This property determines the maximum size of the cache in units that you choose.


For example, if you are using IMemoryCache, you can use the following code to create a cache with a size limit of 100 units:

var cache = new MemoryCache(new MemoryCacheOptions()
{
    SizeLimit = 100
});

STEP 4: To evict items from the cache when the size limit is reached, you need to specify the Size property of each cache entry. This property determines how much space the entry occupies in the cache in units that you choose.


For example, if you are using IMemoryCache, you can use the following code to add an item to the cache with a size of 10 units:

var options = new MemoryCacheEntryOptions()
    .SetSize(10);

cache.Set("key", value, options);

STEP 5: When the cache reaches its size limit, it will remove the least recently used items until enough space is available for new entries. You can also register a callback that is invoked when an item is evicted from the cache by using the PostEvictionCallbacks property of the MemoryCacheEntryOptions class.


For example, log a message when an item is evicted:

var options = new MemoryCacheEntryOptions()
    .RegisterPostEvictionCallback((key, value, reason, state) =>
    {
        var message = $"Cache entry '{key}' was evicted because {reason}.";
        ((ILogger)state).LogInformation(message);
    }, logger);

cache.Set("key", value, options);

Advantages of using this technique:

  • Prevents the cache from consuming too much memory and causing performance issues or unexpected process recycling.

  • Ensures that the most important and frequently used items are kept in the cache and less important and rarely used items are removed when needed.

  • Reduces the number of cache misses and improve the response time of the application.

Disadvantages of using this technique:

  • Requires the developer to choose an appropriate size limit and unit for the cache and each cache entry, which may not be easy or accurate.

  • Requires the developer to assign a priority to each cache entry, which may not reflect the actual usage pattern or importance of the data.

  • Cause some cache entries to be evicted prematurely or unnecessarily, which may result in more database queries or expensive calculations.

Technique 2. Using Sliding and Absolute Expirations

This technique allows you to specify how long a cached item should remain valid based on the time of its last access or the time of its creation. Here are some steps to implement this technique:


STEP 1: If you are using System.Web.Caching.Cache, you can use the Cache.Insert method to add an item to the cache with a sliding or absolute expiration. The sliding expiration is specified by a TimeSpan value that indicates how long the item should remain in the cache after its last access. The absolute expiration is specified by a DateTime value that indicates when the item should expire regardless of its access.


For example, you can use the following code to add an item to the cache with a sliding expiration of 10 seconds and an absolute expiration of 2 minutes:

Cache.Insert("key", value, null, DateTime.Now.AddMinutes(2), TimeSpan.FromSeconds(10));

STEP 2: If you are using System.Runtime.Caching.MemoryCache or IMemoryCache, you can use the MemoryCacheEntryOptions class to configure various aspects of cache entries, such as expiration, priority, size, and dependencies.


For example, add an item to the cache with a sliding expiration of 10 seconds and an absolute expiration of 2 minutes:

var options = new MemoryCacheEntryOptions()
    .SetSlidingExpiration(TimeSpan.FromSeconds(10))
    .SetAbsoluteExpiration(DateTimeOffset.Now.AddMinutes(2));

cache.Set("key", value, options);

STEP 3: When a cached item reaches its sliding or absolute expiration, it will be removed from the cache automatically. You can also register a callback that is invoked when an item is evicted from the cache by using the PostEvictionCallbacks property of the MemoryCacheEntryOptions class.


For example, log a message when an item is evicted:

var options = new MemoryCacheEntryOptions()
    .SetSlidingExpiration(TimeSpan.FromSeconds(10))
    .SetAbsoluteExpiration(DateTimeOffset.Now.AddMinutes(2))
    .RegisterPostEvictionCallback((key, value, reason, state) =>
    {
        var message = $"Cache entry '{key}' was evicted because {reason}.";
        ((ILogger)state).LogInformation(message);
    }, logger);

cache.Set("key", value, options);

Advantages of using this technique:

  • Prevent the cache from consuming too much memory and causing performance issues or unexpected process recycling.

  • Ensure that the cached data is valid and fresh for a certain period of time based on its last access or creation time.

  • Reduce the number of cache misses and improve the response time of the app.

Disadvantages of using this technique::

  • Require the developer to choose an appropriate expiration time for each cache entry, which may not be easy or accurate.

  • Cause some cache entries to expire too soon or too late, which may result in stale or unnecessary data in the cache.

  • Can't handle changes in the external source that invalidate the cached data, such as a file update or a database update.


Technique 3. Using Cache Dependencies and Change Tokens

This technique allows you to invalidate a cached item when a change occurs in an external source, such as a file, a database table, or an options object. Here are some steps to implement this technique:


STEP 1: If you are using System.Web.Caching.Cache, you can use the CacheDependency class to create a dependency between a cached item and a file or a database table. The cache dependency monitors the file or table for changes and removes the cached item when a change is detected.


For example, add an item to the cache with a dependency on a file:

CacheDependency dependency = new CacheDependency("path/to/file");
Cache.Insert("key", value, dependency);

STEP 2: If you are using System.Runtime.Caching.MemoryCache or IMemoryCache, you can use the ChangeMonitor class or its derived classes to create a dependency between a cached item and an external source. The change monitor listens for change notifications from the source and signals the cache when a change occurs.


For example, add an item to the cache with a dependency on a file:

var options = new MemoryCacheEntryOptions();
options.AddExpirationToken(new FileChangeToken("path/to/file"));
cache.Set("key", value, options);

STEP 3: Alternatively, you can use the ChangeToken class to create an IChangeToken object that represents a change token from various sources, such as configuration, file providers, or options. You can then use the AddExpirationToken method of the MemoryCacheEntryOptions class to add the change token to the cache entry.


For example, add an item to the cache with a dependency on an options object:

var options = new MemoryCacheEntryOptions();
options.AddExpirationToken(ChangeToken.OnChange(
    () => _optionsMonitor.GetChangeToken(),
    () => _optionsMonitor.CurrentValue));
cache.Set("key", value, options);

STEP 4: When a cached item has a dependency on an external source, it will be removed from the cache when the source changes. You can also register a callback that is invoked when an item is evicted from the cache by using the PostEvictionCallbacks property of the MemoryCacheEntryOptions class.


For example, log a message when an item is evicted:

var options = new MemoryCacheEntryOptions();
options.AddExpirationToken(new FileChangeToken("path/to/file"));
options.RegisterPostEvictionCallback((key, value, reason, state) =>
{
    var message = $"Cache entry '{key}' was evicted because {reason}.";
    ((ILogger)state).LogInformation(message);
}, logger);
cache.Set("key", value, options);

Advantages of using this technique:

  • Keep the cached data up to date and consistent with the external source, such as a file, a database table, or an options object.

  • Reduce the memory consumption and improve the performance of the cache by removing stale or unused items automatically.

  • Simplify the caching logic by relying on the change notifications from the external source instead of setting expiration times manually.

Disadvantages of using this technique:

  • Require additional code and services to create and monitor the dependencies and change tokens for the cached items.

  • Introduce complexity and overhead when dealing with multiple dependencies and change tokens for a single cache entry.

  • Cause some cache entries to be invalidated prematurely or unnecessarily, which may result in more database queries or expensive calculations.


Technique 4. Using Distributed Caching

This technique allows you to store data in memory across multiple servers that process requests. This way, you can avoid cache consistency problems and handle more load than an in-memory cache. However, you will have to manage the cache size and expiration on your own, as well as handle network latency and serialization costs. Here are some steps to implement this technique:


STEP 1: Choose a distributed cache provider that suits your needs. ASP.NET Core supports several types of distributed cache implementations, such as SQL Server, Redis, and NCache. You will need to install the appropriate NuGet package and configure the connection settings for the cache provider.


STEP 2: Register an implementation of IDistributedCache in Program.cs. This interface provides methods to manipulate items in the distributed cache using byte arrays as values and strings as keys.


For example, register a Redis distributed cache:

services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = "localhost";
    options.InstanceName = "SampleInstance";
});

STEP 3: Use the IDistributedCache service to get or set items in the distributed cache. You will need to serialize and deserialize your objects to and from byte arrays using a serializer of your choice.


For example, get an item from the cache using System.Text.Json:

var value = await _cache.GetAsync("key");
if (value != null)
{
    var item = JsonSerializer.Deserialize<MyItem>(value);
}

STEP 4: Use the DistributedCacheEntryOptions class to configure various aspects of cache entries, such as expiration and sliding expiration.


For example, set an item in the cache with an absolute expiration of one hour:

var options = new DistributedCacheEntryOptions()
    .SetAbsoluteExpiration(TimeSpan.FromHours(1));

var value = JsonSerializer.SerializeToUtf8Bytes(item);
await _cache.SetAsync("key", value, options);

Advantages of using this technique:

  • Improve the performance and scalability of the app by reducing the load on the web servers and the database servers.

  • Avoid cache consistency problems and cache misses when the app is hosted in a cloud or a server farm environment.

  • Survive server restarts and app deployments without losing cached data.

Disadvantages of using this technique:

  • Require additional infrastructure and configuration to set up and maintain the distributed cache service.

  • Incur network latency and serialization costs when accessing the cached data from the web servers.

  • Require manual management of the cache size and expiration, as the distributed cache service does not limit or evict cached items automatically.


Technique 5. Using Custom Cache Providers

This technique allows you to implement your own logic for storing and retrieving data from the cache. You can use custom cache providers when none of the built-in cache implementations meet your requirements or when you want to have more control over the caching behavior. Here are some steps to implement this technique:


STEP 1: Create a class that implements the IMemoryCache or IDistributedCache interface, depending on whether you want to use an in-memory or a distributed cache. You will need to provide your own implementation for the methods defined by the interface, such as Get, Set, Remove, etc.


You can also use other classes or services to help you with the caching logic, such as serializers, timers, change monitors, etc. For example, you can create a custom memory cache class like this:

public class CustomMemoryCache : IMemoryCache
{
    private readonly ConcurrentDictionary<object, CacheEntry> _entries;
    private readonly Timer _timer;

    public CustomMemoryCache()
    {
        _entries = new ConcurrentDictionary<object, CacheEntry>();
        _timer = new Timer(ScanForExpiredItems, null, TimeSpan.Zero, TimeSpan.FromMinutes(1));
    }

    public ICacheEntry CreateEntry(object key)
    {
        var entry = new CacheEntry(key);
        _entries[key] = entry;
        return entry;
    }

    public void Dispose()
    {
        _timer.Dispose();
        _entries.Clear();
    }

    public void Remove(object key)
    {
        _entries.TryRemove(key, out var entry);
        entry?.Dispose();
    }

    public bool TryGetValue(object key, out object value)
    {
        if (_entries.TryGetValue(key, out var entry))
        {
            if (!entry.CheckExpired())
            {
                value = entry.Value;
                return true;
            }
            else
            {
                Remove(key);
            }
        }
        value = null;
        return false;
    }

    private void ScanForExpiredItems(object state)
    {
        foreach (var entry in _entries.Values)
        {
            if (entry.CheckExpired())
            {
                Remove(entry.Key);
            }
        }
    }
}

STEP 2: Register your custom cache provider in Program.cs. You will need to use the AddSingleton method to add your custom cache class as a service that implements the IMemoryCache or IDistributedCache interface.


For example, register a custom memory cache provider:

services.AddSingleton<IMemoryCache, CustomMemoryCache>();

STEP 3: Use the IMemoryCache or IDistributedCache service to get or set items in your custom cache provider. You can use the same methods and options as you would with the built-in cache implementations.


For example, get an item from your custom memory cache provider:

var item = _cache.Get("key");

Advantages of using this technique:

  • More flexibility and control over the caching logic and behavior.

  • Allows to use a cache provider that is not supported by the built-in cache implementations, such as a third-party service or a custom data store.

  • Allow to customize the cache entry options, such as expiration, priority, size, dependencies, etc.

Disadvantages of using this technique:

  • Require more effort and code to implement and maintain your own cache provider.

  • Introduces bugs or errors if your cache provider is not implemented correctly or tested thoroughly.

  • Cause compatibility issues if your cache provider does not follow the same interface or contract as the built-in cache implementations.


Conclusion

Cache overflow scenarios can pose significant challenges to web application performance and functionality. To avoid such scenarios, it is essential to understand the underlying causes of cache overflow and implement effective strategies to handle them in ASP.NET caching. By using a combination of techniques developers can effectively manage cache overflow scenarios and ensure optimal performance for their web applications.

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