ibmcognos.fetchBufferSize

This parameter is used to set the JDBC driver fetch size for data source connections in IBM® Cognos® Analytics.

When the query service in IBM Cognos Analytics executes queries by using JDBC, the fetch size value that is passed to a JDBC driver is calculated dynamically. Support for fetch sizes depends on database vendors. The vendors also decide what the fetch size means, and what the fetch size is when it is used internally in the driver and server. For more details, refer to your vendor’s JDBC documentation.

The query service computes a value for a query by using the following formula: maximum( (bufferSize / ‘row-size’), 10)

The default value for buffer size is 100 kilobytes (KB). The row size is computed from the size of the columns that are projected by the result set in a query. Queries that project columns with large precision or project many columns use a smaller fetch size than those projecting fewer columns or columns with smaller precision.

If the retrieval of a result set can be significantly improved by using a larger buffer size, a Cognos administrator can specify the connection property ibmcognos.fetchBufferSize. The query service automatically adjusts the value if it is lower than 10 kilobytes or greater than 10 megabytes.

If ibmcognos.fetchBufferSize > 1024 * 10240 then bufferSize = 1024 * 10240

If ibmcognos.fetchBufferSize < 10240 then bufferSize = 10240

Larger fetch sizes are not always recommended because they can potentially increase the memory consumption by the JDBC driver and not lead to improved performance. Always review the database vendor documentation and recommended practices before using large values for the ibmcognos.fetchBufferSize property.