The generation of large or complex reports can have a temporary adverse effect on the performance of a ClearSCADA system. We advise that such reports are generated when little communications traffic is expected on a ClearSCADA system—for example in the early hours of the morning.
Although there are no limits to the number of records that ClearSCADA can query, there are limits on the size of the result set that ClearSCADA can return from a single query. By default, this is limited to 1,000,000 rows or 50MB, whichever limit is exceeded first. These limits can be changed on a per system basis, but this may impact on system performance (see Use the Parameters Settings to Define the SQL Query Row and Size Limit in the ClearSCADA Guide to Server Administration).
Furthermore, if a query takes too long to execute, the report may be unable to generate due to the ODBC connection between the Crystal Reports application and ClearSCADA timing out. For this reason, we recommend that you Restrict the Amount of Data that is Queried in a Report, especially if the report queries historic table(s). You may also need to adjust the value of the connection’s Request Timeout property to avoid the ODBC connection timing out (see Define the Port and Poll Timeouts and Intervals for a ViewX Client Connection in the ClearSCADA Guide to Client Administration).