Hi Cheeli,
"broadcast to all AMPs" means sending a message over the BYNET to all AMPs in the system. This has to be done for a NUSI access: the hash of the actual NUSI value can be calculated (using the same algorithm as for base rows), but as the NUSI subtable is not distributed by hash (similar to a NoPI table) the optimizer doesn't know on which AMP this value is located.
When a USI is accessed the AMP on which this value is stored can be calculated and then a point-to-point messsage is send directly to this AMP, which accesses the USI, extracts the base ROWID and send another point-to-pint message to the second AMP. Two times point-to-point is probably much more efficient than sending one message to hundreds, maybe thousands of AMPs and then each AMP has to check for this row.
Dieter
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