SQLRateConnection Function

Version Introduced: ODBC 3.81 Standards Compliance: ODBC

SQLRateConnection determines if a driver can reuse an existing connection in the connection pool.


SQLRETURN  SQLRateConnection(  
                SQLHDBC_INFO_TOKEN   hRequest,  
                SQLHDBC              hCandidateConnection,  
                BOOL                 fRequiredTransactionEnlistment,  
                TRANSID              transId,  
                DWORD *              pRating );  


[Input] A token handle representing the new application connection request.

[Input] The existing connection in the connection pool. The connection must be in an opened state.

[Input] If TRUE, reusing the existing connection's hCandidateConnection for the new connection request (hRequest) requires an additional enlistment.

[Input] If fRequiredTransactionEnlistment is TRUE, transId represents the DTC transaction that the request will enlist. If fRequiredTransactionEnlistment is FALSE, transId will be ignored.

[Output] hCandidateConnection's reuse rating for the hRequest. This rating will be in between 0 and 100 (inclusive).




The Driver Manager will not process diagnostic information returned from this function.


SQLRateConnection produces a score between 0 and 100 (inclusive) indicating how well an existing connection matches the request.

Score Meaning (when SQL_SUCCESS is returned)
0 hCandidateConnection must not be reused for the hRequest.
Any values between 1 and 98 (inclusive) The higher the score, the closer that hCandidateConnection match with hRequest.
99 There are only mismatches in insignificant attributes. The Driver Manager should stop the rating loop.
100 Perfect match. The Driver Manager should stop the rating loop.
Any other value greater than 100 hCandidateConnection is marked as dead and it will not be reused even in an future connection request.

The Driver Manager will mark a connection as dead if the return code is anything other than SQL_SUCCESS (including SQL_SUCCESS_WITH_INFO) or the rating is greater than 100. That dead connection will not be reused (even in future connection requests) and will eventually be timed out after CPTimeout passes. The Driver Manager will continue to find another connection from the pool to rate.

If the Driver Manager reused a connection whose score is strictly smaller than 100 (including 99), the Driver Manager will call SQLSetConnectAttr(SQL_ATTR_DBC_INFO_TOKEN) to reset the connection back into the state requested by the application. The driver should not reset the connection in this function call.

If fRequiredTransactionEnlistment is TRUE, reusing hCandidateConnection needs an extra enlistment (transId != NULL) or unenlistment (transId == NULL). This indicates the cost of reusing a connection and whether the driver should enlist / unenlist the connection if it is going to reuse the connection. If fRequireTransactionEnlistment is FALSE, driver should ignore the value of transId.

The Driver Manager guarantees that the parent HENV handle of hRequest and hCandidateConnection are the same. The Driver Manager guarantees that the pool ID associated with hRequest and hCandidateConnection are the same.

Applications should not call this function directly. An ODBC driver that supports driver-aware connection pooling must implement this function.

Include sqlspi.h for ODBC driver development.

See Also

Developing an ODBC Driver
Driver-Aware Connection Pooling
Developing Connection-Pool Awareness in an ODBC Driver