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Q161634: INF: Connection Pooling Requires Same Henv and Driver

Article: Q161634
Product(s): Open Database Connectivity (ODBC)
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): 
Last Modified: 26-AUG-1999

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The information in this article applies to:

- Microsoft Open Database Connectivity, version 3.0 
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SUMMARY
=======

This article describes the relationships of connection pooling, environments,
and drivers.

MORE INFORMATION
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Connection pooling is one the new features introduced in ODBC 3.0. Connection
pooling enables an ODBC application to reuse a connection from a pool of
connections. Once a connection has been created and placed in the pool, an ODBC
application can reuse the same driver and the connection within the same
environment (henv) without performing the complete connection process.
Connection can never be reused between different henv or different drivers.

You can use the SQLSetEnvAttr function call to enable connection pooling. There
are two attributes available for connection pooling under the SQLSetEnvAttr
function: SQL_CP_ONE_PER_HENV and SQL_CP_ONE_PER_DRIVER. The difference between
these two attributes is a performance/comparison consideration, and the use of
any one of these options does not change which connection is reused.

With the SQL_CP_ONE_PER_HENV attribute, a comparison pool is created for each
henv. The pool may include connections from different drivers within the same
environment. The ODBC driver manager searches this pool for the driver that
matches the requested connection. You normally use this option if there are many
henvs but few drivers, because it saves you the number of comparisons (with the
cost of memory for the pools).

With the SQL_CP_ONE_PER_DRIVER attribute, a comparison pool is created for each
driver. The pool may include different henvs that use the same driver. The ODBC
driver manager searches this pool for the henv that matches the requested
connection. You normally use this option if there are many drivers but few
henvs, for the same reason in the previous paragraph.

The ODBC 3.0 API online Help version 4.00.950 mistakenly states that you can
share connections between different environments with the SQL_CP_ONE_PER_HENV
attribute. Connections can only be reused within the same henv and the same
driver. Connections can never be reused between different henvs or different
drivers.

Additional query words: viper sql memory leak

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Keywords          :  
Technology        : kbAudDeveloper kbODBCSearch kbODBC300
Version           : WINDOWS:3.0

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