connection-pool.md

Connection Pooling

StackExchange.Redis.Extensions is based on top of StackExchange.Redis and of course, for the connection part, offers all the main library has but with a bounce of more features like ConnectionPool and MaxMessageSize.

The importance of Connection pool.

The connection pool is one of the most helpful features that this library offers because is some case can save you from the annoying timeout. Here the complete documentation of the most common reason why you can get a timeout using Redis, but below you can find a summary:

because StackExchange.Redis uses a single TCP connection and can only read one response at a time. Even though the first operation timed out, it does not stop the data being sent to/from the server, and other requests are blocked until this is finished. Thereby, causing timeouts. One solution is to minimize the chance of timeouts by ensuring that your redis-server cache is large enough for your workload and splitting large values into smaller chunks. Another possible solution is to use a pool of ConnectionMultiplexer objects in your client, and choose the "least loaded" ConnectionMultiplexer when sending a new request. This should prevent a single timeout from causing other requests to also timeout.

With StackExchange.Redis this comes out of the box and you don't have to do anything except increase the size of the pool if you need it.

Our Redis client wrapper includes an additional feature for connection pooling. Connection pooling can greatly improve the performance of your application by distribuiting the load across multiple connections.

To do this, the client undertakes to create a series of active connections to the server so that they are ready when their use is needed.

Benefits of Connection Pooling

• Improved performance: Connection pooling reduces the time spent in opening and closing connections, thereby improving the performance of command execution.
• Optimized use of resources: By reusing existing connections, connection pooling helps to save system resources. It limits the number of simultaneous connections, reducing the memory usage and load on your database.

Disadvantages

Depending on the size of the pool, the client, on startup, opens a connection to the server.

This means that the higher the pool size the longer the application startup time and the number of connections used.

Connection Selection Strategies

Our Redis client wrapper supports two strategies for selecting connections from the pool that you can select into the RedisConfiguration:

var redisConfiguration = new RedisConfiguration()
{
    AbortOnConnectFail = false,
    KeyPrefix = "MyPrefix__",
    Hosts = [
        new RedisHost
        {
            Host = "localhost",
            Port = 6379
        }
    ],
    AllowAdmin = true,
    ConnectTimeout = 3000,
    Database = 0,
    PoolSize = 2,
    ConnectionSelectionStrategy = ConnectionSelectionStrategy.LeastLoaded,
    ServerEnumerationStrategy = new()
    {
        Mode = ServerEnumerationStrategy.ModeOptions.All,
        TargetRole = ServerEnumerationStrategy.TargetRoleOptions.Any,
        UnreachableServerAction = ServerEnumerationStrategy.UnreachableServerActionOptions.Throw
    }
};

The important part is the ConnectionSelectionStrategy property.

RoundRobin

With this strategy, each call returns the next connection in the pool in a round-robin manner. This strategy is useful for distributing the load evenly across all the connections. (more information about round robine is available here)

LeastLoaded

This strategy returns the least loaded connection for each call. The load of a connection is defined by its ServerCounters.TotalOutstanding. This strategy is effective in scenarios where the load is unevenly distributed among connections.

The default strategy is LeastLoaded.

When to Use Connection Pooling

Connection pooling is particularly beneficial for applications with high traffic, where opening and closing connections frequently can significantly impact performance and there are lot of concurrent operation from the client to the server.

For more information on how to configure the connection pool and set up the selection strategy, refer to the 'Configuration' section of our application.