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Why Multiload does not supports USI and supports NUSI?
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Answer Posted / reddy
MulitLoad has support for Non-Unique Secondary Indexes
(NUSIs) since NUSIs are AMP Local. They have subtable
within base table. It has no hash bucket to redirect to
another amp, everything points to their own amp (AMP Local)
If you go with USI, it has hash bucket, which might
redirect to another amp, more possibilites for full table
scan.
Motive for avoiding Indexes(other thn NUSI): Avoid Full
table scan. whenever we define a SI an SI subtable is
created in each AMP.For USI they go for a hash
distribution, and hence the actual data row pointed by the
USI subtable rows in one AMP may not be in the same AMP as
the subtable..so the AMPs
have to communicate, which is not supported by Multiload.
For NUSI the subtable will store references of only those
actual data rows who exist in the same AMP as the
subtable..they all point to the data in their own
AMP..hence AMPs dont need to communicate here.
Thus the AMPs work in parallal with NUSI and hence Mload
supports that.
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