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The IBM Toolbox for Java JDBC properties list the property "big decimal". When set to "true" it returns a Kettle data type of a BigNumber instead of a Number that could help in specific cases. It is recommended to set this option to "true" due to possible rounding issues with Numbers (double precision values), but has a small performance impact.
Monitoring
Have a look at the QZDASOINIT jobs at the AS/400. These jobs are serving the database SQL server jobs for JDBC and looking into these give a lot of extra information.