An application pool is a configuration that links one or more applications to a set of one or more worker processes. Because applications in an application pool are separated from other applications by worker process boundaries, an application in one application pool is not affected by problems caused by applications in other application pools.
By creating new application pools and assigning Web sites and applications to them, you can make your server more efficient and reliable, as well as making your other applications always available, even when the worker process serving the new application pool has problems.
A database connection pool is a set of database connections that are held open with the database and are kept ready to serve. This way, a set of connections is created once the pool comes into existence. When a user requests a connection, an already created connection is served from the pool. Similarly, when a user closes a connection, it is returned to the pool instead of being destroyed. This can significantly improve the performance of data access.
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