Use Single Transaction Option / MergeTransactions Property Not Limiting To Single Transaction

Question

I have a SSRS report which contains a List. Within the List is a sub-report. Although the option "use single transaction when processing the queries" has been selected for the Data Sources of all reports/sub-reports, and all reports use the same
Shared Data Source, multiple transactions are utilized. I have also set the MergeTransactions property of every SubReport to True.
It is critical that the report use only one connection to the Data Source when it is executed (limited licensing issue with old DBMS - UniData).
For my other SSRS reports, which contain sub reports but the sub reports are not within a List, the "use single transaction when processing the queries" option works as expected and a single connection is made to the Data Source when the report
is executed.
Is there something I can do to force a single transaction to be used in this situation? I am running SQL Server 2008 R2 Enterprise Edition SP3. I found this fix for the problem for SQL Server 2008: kb 974404 (won't let me insert links).
Thanks, Kevin

Answer 1

Wendy,
Thank you for responding. The reports all use the same shared datasource. However, they do not use shared datasets. Each DataSet calls an SQL Server Stored Procedure located in the same SQL Server Database. When this report is executed, multiple connections
are opened to the DBMS from which the data is actually fetched, which can only occur of SSRS is executing multiple Stored Procedures in parallel. I have confirmed this behavior by logging which Stored Procedures are executed and when. I have confirmed the
behavior in the other DBMS by running a command which lists all licenses used. Several connections are listed from the User which is used exclusively for the SSRS reporting. All of these connections are opened at the same time (within fractions of
a second) that execution of the SSRS report begins.
As to whether multiple transactions are used by SSRS, I can only assume they are, since multiple connections are opened and queries are executed concurrently. I should state again that I am concerned about connections made, not transactions in SQL Server.
I have many other reports, some of which call the same Stored Procedures as the problematic report. When these other reports are executed, and the "use single transaction..." and MergeTransactions options are set, only one connection is opened though
several queries are executed. It is only when a sub report is placed in a list that multiple connections are made and queries are executed concurrently even though the afore mentioned options are set.
I can provide further details about the DBMS where the data reported on resides and how queries are executed against this database from an SQL Server Stored Procedure if you require it. However, I have ensured there is no parallel code and that SSRS is initiating
the concurrent connections by executing the Stored Procedure which the Sub Report reports on multiple times in parallel. I can also provide the report definitions if you need them.
Thanks,
Kevin