Hi Vikram,
#1: the optimizer knows about the system (number of AMPs, CPU speed, etc.) and this is included in planning, so yes, it's dependent on the number of AMPs
#2: There are many different ways to prepare data for a join, the optimizer will calculate which is the least expensive one.
#3: Of course it might degrade performance (and it will in probably most cases), it's just to check hwo the plan will look like when the PI is changed
You'll find lots of info about planning/optimization in the "SQL Request and Transaction Processing" manual.
Btw, those questions are not silly :-)
Dieter
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