This process of closing and creating connection may slow down your application and reduce its performance. When using a single connection, the queries have to be simple. Otherwise, their execution will slow down the application and decrease its performance. Hence the limited number of users at the same time. Also, a new connection is created for each new query and we all know that opening and maintaining a database connection is costly and heavy task. The biggest issue of a single connection is when the connection is closed suddenly and you did not take this into account in your implementation.
In connection pooling, a connection can be an active connection or an available connection. When a new connection is created, it is placed in the pool and used to execute the query has just arrived. After execution, the application closes the connection, so pool is notified that the connection is available and ready for reuse. Having connections created in advance reduce the user waiting time needed to create new connection to execute new queries.
When an application requests a connection from the connection pool, the Pool assigns an available connection. If an unused connection exists, the pool return it. Connections are released back into the pool when they are closed or disposed. When a SqlConnection object is requested, it is obtained from the pool if a usable connection is available. To be usable, a connection must be unused, have a matching transaction context or be unassociated with any transaction context, and have a valid link to the server.
The connection pooler satisfies requests for connections by reallocating connections as they are released back into the pool. If the maximum pool size has been reached and no usable connection is available, the request is queued. The pooler then tries to reclaim any connections until the time-out is reached the default is 15 seconds.
If the pooler cannot satisfy the request before the connection times out, an exception is thrown. We strongly recommend that you always close the connection when you are finished using it so that the connection will be returned to the pool.
You can do this using either the Close or Dispose methods of the Connection object, or by opening all connections inside a using statement in C , or a Using statement in Visual Basic. Connections that are not explicitly closed might not be added or returned to the pool. Do not call Close or Dispose on a Connection , a DataReader , or any other managed object in the Finalize method of your class.
In a finalizer, only release unmanaged resources that your class owns directly. If your class does not own any unmanaged resources, do not include a Finalize method in your class definition. For more information, see Garbage Collection. The connection pooler removes a connection from the pool after it has been idle for approximately minutes, or if the pooler detects that the connection with the server has been severed. Note that a severed connection can be detected only after attempting to communicate with the server.
If a connection is found that is no longer connected to the server, it is marked as invalid. Invalid connections are removed from the connection pool only when they are closed or reclaimed. If a connection exists to a server that has disappeared, this connection can be drawn from the pool even if the connection pooler has not detected the severed connection and marked it as invalid.
This is the case because the overhead of checking that the connection is still valid would eliminate the benefits of having a pooler by causing another round trip to the server to occur. When this occurs, the first attempt to use the connection will detect that the connection has been severed, and an exception is thrown.
NET 2. ClearAllPools clears the connection pools for a given provider, and ClearPool clears the connection pool that is associated with a specific connection. If there are connections being used at the time of the call, they are marked appropriately. When they are closed, they are discarded instead of being returned to the pool. Connections are drawn from the pool and assigned based on transaction context. Connecting to a backend service is an expensive operation, as it consists of the following steps:.
In a production environment where we expect thousands of concurrent open and close connections from clients, doing the above steps for every single connection can cause the database to perform poorly.
We can resolve this problem by pooling connections from clients. Instead of creating a new connection with every request, connection poolers reuse some existing connections. Thus there is no need to perform multiple expensive full database trips by opening and closing connections to backend service.
It prevents the overhead of creating a new connection to the database every time there is a request for a database connection with the same properties i. Pooling middleware like pgbouncer comes with a pool manager. Usually, the connection pool manager maintains a pool of open database connections.
You can not pool connections without a pool manager. When a new request to access data from the backend service comes in, the pool manager checks if the pool contains any unused connection and returns one if available. If all the connections in the pool are active, then a new connection is created and added to the pool by the pool manager. When the pool reaches its maximum size, all new connections are queued until a connection in the pool becomes available. Although most databases do not have an in-built connection pooling system, there are middleware solutions that we can use to pool connections from clients.
For a PostgreSQL database server, both pgbouncer and pgpool-II can serve as a pooling interface between a web service and a Postgres database. Both utilities use the same logic to pool connections from clients.
Connection poolers such as pgbouncer and pgpool-II can be used to pool connections from clients to a PostgreSQL database. The connection pooler sits in between the application and the database server. Pgbouncer or pgpool-II can be configured in a way to relay requests from the application to the database server. There exist libraries such as c3p0 which extend database driver functionality to include connection pooling support.
However, the best way to implement connection pooling for applications is to make use of an external service or middleware since it is easier to set up and manage. In addition external middleware like pgpool2 provides other features such as load balancing apart from pooling connections. We do not need a connection pooler to connect to a backend service.
We can connect to a Postgres database directly. To examine how long it takes to execute concurrent connections to a database without a connection pooler, we will use pgbench to benchmark connections to the Postgres database. Pgbench is based on TPC-B. TPC-B measures throughput in terms of how many transactions per second a system can perform. Based on TPC-B-like transactions, pgbench runs the same sequence of SQL commands repeatedly in multiple concurrent database sessions and calculates the average transaction rate.
Pgbench uses the following tables to run transactions for benchmarking. As you see, in our initial baseline test, I instructed pgbench to execute with ten different client sessions.
Each client session will execute 10, transactions. From these results, it seems our initial baseline test is transactions per second. Pgbouncer can be installed on almost all Linux distributions. Create a free Team What is Teams?
Collectives on Stack Overflow. Learn more. Why should I use connection pooling? Ask Question. Asked 9 years ago. Active 9 years ago. Viewed 4k times. Open ; Most samples on the net make use of the 'connect and close' construction above. Q: Why should I use connection pooling? Improve this question. I don't understand, 14 seconds is faster than 15 seconds, isn't it? You just said that with connection pooling your queries take 14 instad of 15 seconds.
How is that "slower"? Probably a typo Add a comment. Active Oldest Votes.
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