ODBC Connection Pooling

The following applies to ODBC connection pooling:

Connections are pooled by ODBC data source. If a data source is used by one or more user directories AND (the policy store or another store on the policy server), the number of connections available may reach the total of the individual values specified for user directories and stores.
SQL Server is more limited than Oracle in how connections may be shared. Two callers may not share an open result set while the results are being fetched to the client. Although the Policy Server uses server side cursors for SQL Server, there are limitations to concurrent activity, especially on multi-processor machines. Increasing the number of connections will generally improve concurrency.
Oracle allows for multiple callers to share a connection, but may serialize calls internally. Again, you may see improved concurrency by increasing the number of connections allowed.
If connections are shareable, the number of active requests will be balanced across the connections in a pool.
Once a connection is opened, it is not closed until the Policy Server is shut down.