Connection pooling may improve the performance of applications that make multiple, brief connections to the database server.
If connection pooling is enabled for a connection, when it is disconnected, the connection is automatically cached and may be reused when the application reconnects. For server-side connection pooling, enable pooling with the ConnectionPool (CPOOL) connection parameter. Once an application makes a specified number of connections with the same connection string, then the connection is pooled.
For connection pooling in .NET applications, use the .NET Pooling connection parameter - the ConnectionPool (CPOOL) connection parameter is ignored. The .NET Data Provider cleans up and reinitializes pooled connections.
An application must make five connections with the same connection string before a connection is cached. The connection name can be different each time, but all other connection parameters must be identical for a cached connection to be reused.
If the application process connects again and there are cached connections available for the same connection string, the cached connection is reused. Connections remain in the cached state for the time specified by the ConnectionPool (CPOOL) connection parameter (60 seconds by default).
Connection pooling does not occur for non-standard database authentication such as Integrated or Kerberos logins. Only user ID and password authentication is supported.
Cached connections are not reused if it would change the behavior of the application. For example, cached connections are not reused:
For databases that stop automatically when there are no connections to them.
If connections are disabled.
If the database server has reached its connection limit.
If a password has changed.
If the login_mode option is set.
To ensure that connection pooling is transparent to the application, a connection is disconnected if a failure occurs when caching a connection. If a failure occurs when attempting to reuse a cached connection, the database server attempts to connect normally.
A connection is cached if it is disconnected and the maximum number of connections specified by the CPOOL connection parameter has not been reached. The connection is reinitialized, and the cached connection continues to be connected to the database server even though the application has disconnected it. The cleanup and reinitialization of a connection includes the following activities:
Rolling back all outstanding transactions.
Dropping temporary tables, temporary functions, and variables.
Resetting connection options and connection counters.
Decrementing and incrementing the database server connection counts. You are not informed that there are active connections when a database server with only cached connections shuts down.
Executing all defined disconnect and connect events.
Executing the login_procedure database option and verifying the login policy.
Resetting the connection ID.
If you are using a product or API that supports connection pooling, then the connection pooling of the product or API supersedes SQL Anywhere connection pooling. Both types of connection pooling can be active at the same time.
The behavior of connection pooling in your product or the API may be significantly different than SQL Anywhere connection pooling. If the behavior of connection pooling in your product or API is inappropriate for an application, SQL Anywhere connection pooling can be used and may improve the performance of some applications.
If the NodeType (NODE) connection parameter is also specified for a connection, the application typically connects to the primary server and the primary server determines which copy node is least heavily loaded. The connection is then redirected to that node. If the application makes and drops several such connections within a short period of time, the connection is pooled and the primary server is not asked which copy node to use. This behavior reduces the load on the primary server, but may not give expected behavior.