Sql connection pool

Connecting to a database server typically consists of several time-consuming steps. A physical channel such as a socket or a named pipe must be established, the initial handshake with the server must occur, the connection string information must be parsed, the connection must be authenticated by the server, checks must be run for enlisting in the current transaction, and so on. In practice, most applications use only one or a few different configurations for connections. This means that during application execution, many identical connections will be repeatedly opened and closed.

To minimize the cost of opening connections, ADO. NET uses an optimization technique called connection pooling. Connection pooling reduces the number of times that new connections must be opened. The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks for an available connection in the pool.

If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of closing it.

Once the connection is returned to the pool, it is ready to be reused on the next Open call. Only connections with the same configuration can be pooled. NET keeps several pools at the same time, one for each configuration. Connections are separated into pools by connection string, and by Windows identity when integrated security is used. Connections are also pooled based on whether they are enlisted in a transaction.

When using ChangePasswordthe SqlCredential instance affects the connection pool. Different instances of SqlCredential will use different connection pools, even if the user ID and password are the same. Pooling connections can significantly enhance the performance and scalability of your application. By default, connection pooling is enabled in ADO.

Unless you explicitly disable it, the pooler optimizes the connections as they are opened and closed in your application. You can also supply several connection string modifiers to control connection pooling behavior.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I stil have a doubt asp. I work on a application that sometimes throws the exception "max pool size was reached". But, now it comes my doubt. When it says "max pool size was reached", does it mean that max pool size was reached for the database or for the server? If SQL Server hosts several databases for several differents asp. NET maintains separate connection pool groups per connection string.

So if you have multiple databases, they should have their own pools, and those pools should not interfere with each other. Is it possible that some requests are taking a long time? If enough requests are executed at once against a single database, and they are delayed, maybe the connection pool really is being reached simply because of open connections. You can also query the DMVs in the database to see how many connections various programs have open by database:. If you did find out that you just need more connections, you can tweak the limit in the connection string by setting the property Max Pool Size to something other than Here is an example.

It is possible to dig through the. NET objects in a debugging heap if you want to see what pool is causing the problem. You would have to capture a memory dump of the w3wp.

What is a SQL Server connection pooling in C#? – Querychat

I have done this in the past. It is not necessarily easy, but it can help a lot. There is a perfmon counter for ADO. NET connection pooling that you can use to monitor leaking connections.

In Performance Monitor, cxpand. According to the documentation, this counter means:. The number of connections that have been reclaimed through garbage collection where Close or Dispose was not called by the application.

Not explicitly closing or disposing connections hurts performance. Learn more. Asked 6 years, 7 months ago. Active 5 years, 2 months ago. Viewed 2k times.

Elastic pools help you manage and scale multiple databases in Azure SQL Database

Good evening! My team looked over and over for some code that was leaking but nothing was found.One of those aspects is connection pooling. The answer that enterprise DBAs need to be giving to these inquiries is that it is provider-specific.

I will show an example of this below using the. SqlClient namespacebut the ideas proposed should propagate to other popular providers used today. An application utilizes a provider to make connections to an instance of SQL Server. The above connection string is rather simple, but I am specifying the Application Name parameter so that we can easily parse sys. SqlConnection objects:. All this does is instantiate the SqlConnection objects utilizing the same connection string that we defined above.

Note: Connection Pools are going to be defined by the connection strings that are passed. Different connection strings, different connection pools. Now we want to open these connections.

I put a two second sleep in between each connection opening just to see a gradual increase in the pooled connection count with the PerfMon counter NumberOfPooledConnections for all instances of the.

SQL Server Connection Pooling (ADO.NET)

Looking at the aforementioned counter in PerfMon, we see that the number of pooled connections goes from zero to five within the ten second duration. We can also see this from sys.

Now, there is nothing new here. There have been five connections, and there are five sessions that show this. But connection pooling comes into play and really flexes its muscles when these connections are closed, and even disposed:. But, re-executing the sys. This is connection pooling. PerfMon also shows us that these connections are indeed in the pool for later reuse:.

Modifying only the application name in the connection string, I create a new one and specify this for two more connections:. Glancing back at the PerfMon counters I have now added the NumberOfActiveConnectionPools counterwe see that these two new connections are in a separate connection pool due to a different connection string:. It is one for the first five connections, as they all use the same connection string. Specifying a different connection string for two additional connections show us that the five original connections cannot be reused, so another connection pool is created for this new connection string, and now holds the two new connections.

One of the biggest considerations with connection pooling is to ensure that proper disposal or closure of the SqlConnection object s is taking place.

sql connection pool

A list of connection string parameters, including those related to connection pooling, can be found on the MSDN reference for the SqlConnection. ConnectionString property. OpenI received the following error, describing quite well what probably happened and in this case, did happen :. This is a common pitfall for web applications, and the above example illustrates why this can be a problem.

Say a web application uses the default max pool sizeand there are currently active and consumed pooled connections. Because they may not have been properly closed or disposed, the th attempt will result in a similar error and behavior. Dispose method at the end of the block. Like with many diagnosing and monitoring requirements, we can see connection pooling or the lack thereof with SQL Trace or Extended Events.

You would see similar results:.The following example creates a SqlCommand and a SqlConnection. The example then calls ExecuteNonQuery. The connection is closed automatically when the code exits the using block. When you create an instance of SqlConnectionall properties are set to their initial values. For a list of these values, see the SqlConnection constructor.

See ConnectionString for a list of the keywords in a connection string. If the SqlConnection goes out of scope, it won't be closed. Therefore, you must explicitly close the connection by calling Close or Dispose. Close and Dispose are functionally equivalent.

If the connection pooling value Pooling is set to true or yesthe underlying connection is returned back to the connection pool. On the other hand, if Pooling is set to false or nothe underlying connection to the server is actually closed.

Login and logout events will not be raised on the server when a connection is fetched from or returned to the connection pool, because the connection is not actually closed when it is returned to the connection pool. To ensure that connections are always closed, open the connection inside of a using block, as shown in the following code fragment. Doing so ensures that the connection is automatically closed when the code exits the block.

To deploy high-performance applications, you must use connection pooling. When you use the.

Working with a connection

NET Framework Data Provider for SQL Server, you do not have to enable connection pooling because the provider manages this automatically, although you can modify some settings. If a SqlException is generated by the method executing a SqlCommandthe SqlConnection remains open when the severity level is 19 or less. When the severity level is 20 or greater, the server ordinarily closes the SqlConnection.

However, the user can reopen the connection and continue. An application that creates an instance of the SqlConnection object can require all direct and indirect callers to have sufficient permission to the code by setting declarative or imperative security demands. SqlConnection makes security demands using the SqlClientPermission object. Users can verify that their code has sufficient permissions by using the SqlClientPermissionAttribute object.

Users and administrators can also use the Caspol. For more information, see Security in. For more information about handling warning and informational messages from the server, see Connection Events. You can force TCP instead of shared memory.

sql connection pool

You can do that by prefixing tcp: to the server name in the connection string or you can use localhost. Initializes a new instance of the SqlConnection class. Initializes a new instance of the SqlConnection class when given a string that contains the connection string. The connection ID of the most recent connection attempt, regardless of whether the attempt succeeded or failed.In this article, we will discuss what a SQL Server connection pooling is, and how it works in Cincluding a brief explanation on how to execute it, with simplified examples.

When an application access a database, for every time it connects, it will create a new connection. This will need several more steps to establish communication, which can influence the overall performance. NET has an optimization practice, which is the connection pooling, that helps to minimize the number of open connections. The main principle that the connection pooling uses is to limit the number of newly opened connections.

Depending on the connection configuration, there will be several connection pools. There are several ways to differentiate a connection, which could be by its Windows identity, or by its connection string. For the following example, we will create two different pools by assigning two values for the Initial Catalog, which creates two different connection strings:. For the following example, we will create one pool by assigning the same value for the Initial Catalog, which will maintain the same connection string:.

For the following example, we will clean all pools using the ClearAllPools method, create one pool by assigning the same value for the Initial Catalog, and finally clear only the pool connection that was created:. There are several considerations while working with connection pools, which are the following:. Your SQL questions, answered. Examples Example 1. Keep in mind if the MinPoolSize variable is not set or its value is zero, the opened connection will close after it enters an inactivity period.

If this variable is set to a value greater than zero, then the opened connection will not close until the execution ends. If a new connection is requested and there are no available ones, the connection pool will search for any usable connection until the time limit is reached which is 15 seconds as a default. If this happens, an exception will be thrown.

If an available connection in the connection pool has been idle around four to eight minutesit will be removed from the pool. This can also happen if a connection is no longer communicating to the server, and it will be considered as an invalid connection, but will not be removed until the connection is closed. To clean the connection pools, ADO. The ClearPool method will only clean a specific pool connection, while the ClearAllPools method will clean all the pools that are considered for a specific provider.

When the methods are executed, and there are opened connection under the specific connection pool that we want to clear, then it will be marked to be discarded after it the connection is closed. Related blogs. This comment form is under antispam protection. Notify of. Trusted by people who work at. This feature is not available yet! Please check again in the near future.This technique will create a database connection using the first available driver in the list of drivers that can successfully connect with the given URL.

When using the sqljdbc4. When the getConnection method of the DriverManager class is called, an appropriate driver is located from the set of registered JDBC drivers. If you have to specify a particular driver in the list of drivers for DriverManager, you can create a database connection by using the connect method of the SQLServerDriver class, as in the following:.

If you have to create a connection by using the SQLServerDataSource class, you can use various setter methods of the class before you call the getConnection method, as in the following:. If you have to make a database connection that targets a specific data source, there are a number of approaches that you can take.

Each approach depends on the properties that you set by using the connection URL. If you have to adjust for server load or network traffic, you can create a connection that has a specific login timeout value described in seconds, as in the following example:. If you have to use logging and profiling, you will have to identify your connection as originating from a specific application, as in the following example:.

You can explicitly close a database connection by calling the close method of the SQLServerConnection class, as in the following:. This will release the database resources that the SQLServerConnection object is using, or return the connection to the connection pool in pooled scenarios. Skip to main content. Contents Exit focus mode. Note When using the sqljdbc4.

Using sql server with entity framework core

Note Calling the close method will also roll back any pending transactions. Is this page helpful? Yes No. Any additional feedback? Skip Submit. Submit and view feedback for This product This page. View all page feedback.This tip will help you to better understand what connection pooling is in the data access world. Also, after reading this tip, you will have more knowledge on how to take advantage of the connection pooling mechanism when writing.

sql connection pool

In its simplest explanation, a connection pool is a cache of database connections. NET connection pooling and even more specifically, we will talk about how you can take advantage of SQL Server connection pooling from your. NET application i. At this point it is worth mentioning that connection pooling is a mechanism widely supported in software engineering and is supported by all major DBMSs.

NET, connection pooling is automatically used under certain conditions.

sql connection pool

Understanding the benefits of connection pooling and how it works, can help you manage your database connections when writing data access code more efficiently, thus enabling your application to be more performant and robust. In a few words: for performance, for application stability, for avoiding exhaustion of database connection pools, and more.

For example, in order to establish a single database connection from a C program to a SQL Server instance, there is a series of steps that takes place in the background. These steps can include: establishing the actual network connection to a physical channel i. Now, imagine having an application opening and closing database connections all the time or even worse; not closing the database connectionswithout reusing at least some of the already cached database connection pools.

In some cases, this could be a situation that would lead to an exhaustion of database connection pools, and consequently would possibly lead to an application crash if not proper exception handling is in place. NET provides connection pooling capabilities with the use of a pooler. This pooler manages connections by keeping alive a number of established connections for any given connection configuration in the data application that uses ADO.

A connection configuration is actually the connection string used for that connection. This saves time and resources. The information above covered the theory behind the connection pooling technique.

We see that there are currently not any connections on any of the above databases in SQL Server:. We check again the Activity Monitor in SQL Server Management Studio and we can see that, as expected, there are three connections established each one to the respective sample database:.

So far, so good. As expected, we get 3 different database connections because our code had 3 different connection strings. No connection pooling was applicable for the above scenario. Just to confirm that by the time the application closes, the database connections are terminated as well, you can check the below screenshot:. NET connection pooling is all about!


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