10 SQL Server Connection Pooling Best Practices

SQL Server connection pooling is a great way to improve the performance of your application. By reusing existing connections, your application can avoid the overhead of creating new connections each time it needs to communicate with the database.

However, connection pooling is not a silver bullet. There are a number of factors that can impact the performance of your application when using connection pooling. In this article, we will discuss 10 best practices that you can follow to ensure that your application is getting the most out of SQL Server connection pooling.

1. Use connection pooling

When you use connection pooling, your application can reuse existing connections instead of creating new ones, which reduces overhead and improves performance. In addition, connection pooling can help reduce the number of open connections to your database, which can free up resources and improve overall stability.

To take advantage of connection pooling, you need to configure your application to use a connection pool provider, such as the SQL Server .NET Data Provider or the ODBC .NET Data Provider. You can also use third-party connection pool providers.

Once you’ve configured your application to use a connection pool provider, you need to specify the connection string for your database. The connection string must include the following parameters:

* `Pooling` – Set this to `true` to enable connection pooling.
* `Min Pool Size` – The minimum number of connections that will be maintained in the pool.
* `Max Pool Size` – The maximum number of connections that will be maintained in the pool.

You can optionally specify other parameters, such as the `Connection Lifetime`, which controls how long a connection can stay in the pool before it is closed.

By default, the SQL Server .NET Data Provider uses the System.Data.SqlClient connection pool provider. To use a different provider, you can specify the `Provider` parameter in the connection string. For example, to use the ODBC .NET Data Provider, you would specify `Provider=MSDASQL`.

2. Set the Min Pool Size to 0

When the Min Pool Size is set to 0, the SQL Server connection pool will automatically shrink when it’s not being used. This is important because it helps reduce the number of open connections to the SQL Server, which can help improve performance.

It’s also a good idea to set the Max Pool Size to a value that’s larger than the Min Pool Size. This way, if the SQL Server connection pool does need to grow, it will have room to do so.

3. Set the Max Pool Size to 100

The Max Pool Size is the maximum number of connections that can be open at any given time. By default, the Max Pool Size is set to 100 in SQL Server. However, many organizations leave this setting at the default, which can lead to connection issues.

If the Max Pool Size is too low, your application will experience connection errors because there are not enough connections available. On the other hand, if the Max Pool Size is too high, you may end up with a lot of idle connections that are taking up resources and not being used.

The best practice is to set the Max Pool Size to 100. This gives you a good balance between having enough connections available and not having too many idle connections.

4. Set Connection Lifetime to 0

When a connection is returned to the pool, its creation time is compared to the current time. If the difference (in seconds) exceeds the value specified by Connection Lifetime, the connection is destroyed and a new one is created when requested. This ensures that only “fresh” connections are used, and helps prevent issues caused by stale connections.

If you’re not sure what value to use for Connection Lifetime, start with 0 and adjust as needed.

5. Set Load Balance Timeout to 0

When a SQL Server connection is opened, it’s assigned to a specific server instance. If that server instance becomes unavailable, the connection will be failed over to another server instance. However, if Load Balance Timeout is greater than 0, the connection will not be failed over and will instead timeout.

By setting Load Balance Timeout to 0, you are ensuring that connections are failed over as soon as the server instance becomes unavailable. This helps to avoid any downtime for your applications.

6. Set Connect Timeout to 15 seconds

If you don’t set Connect Timeout to 15 seconds, your application will wait for 30 seconds (the default value) before timing out and throwing an exception. That’s a long time for your application to be unresponsive, and it could cause your users to lose patience and go elsewhere.

Setting Connect Timeout to 15 seconds ensures that your application won’t be unresponsive for more than 15 seconds, and it also allows you to troubleshoot any connection issues more quickly.

7. Set Inactive Connection Resiliency to 10 minutes

If a SQL Server connection is inactive for more than 10 minutes, the chances are high that the server has been restarted or the network has gone down. In either case, the connection is no longer valid and should be discarded. By setting Inactive Connection Resiliency to 10 minutes, you ensure that connections are regularly checked for validity and that invalid connections are discarded quickly.

This best practice can help prevent errors such as “The connection was not closed. The connection’s current state is open.”

8. Disable MARS (Multiple Active Result Sets)

MARS is a feature that allows multiple queries to be executed on a single connection. While this may sound like a good idea, it can actually lead to significant performance issues because the connection pool has to manage multiple queries at the same time.

Not only does this make the connection pool less efficient, but it can also cause deadlocks and other problems. For these reasons, it’s best to disable MARS and use separate connections for each query.

9. Don’t use a DataReader with a CommandBehavior of CloseConnection

When you use the CommandBehavior of CloseConnection with a DataReader, it tells the SQL Server to close the connection when the DataReader is closed. This might not seem like a big deal, but it actually is.

The reason it’s a big deal is because when the connection is closed, it’s removed from the connection pool. So, if you have a lot of users using your application, and they’re all using the DataReader with the CommandBehavior of CloseConnection, then your connection pool is going to be constantly emptying and refilling itself, which is going to cause a performance hit on your application.

Instead, you should use the CommandBehavior of Default, which will keep the connection open when the DataReader is closed. This way, the connection can be reused by another user, and your connection pool will stay full, which will improve the performance of your application.

10. Don’t call Close or Dispose on your connections

When you call Close or Dispose on a connection, the connection is actually removed from the pool and destroyed. This means that the next time you try to retrieve a connection from the pool, a new one will be created, which incurs the overhead of creating a new connection.

It’s better to simply return the connection to the pool so it can be reused. The pool will take care of closing and disposing of the connection when it’s no longer needed.