Hi frinds pls help me regarding this question WHY usi is two amp operation in

Hi frinds pls help me regarding this question

WHY usi is two amp operation in teradata?
THANKS IN ADVANCE....

Question Posted / gowthami8.b

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Hi frinds pls help me regarding this question WHY usi is two amp operation in teradata? THANKS I..

Answer / tdguy

When an USI is created, a subtable is generated and stored.
When that USI is used in the query,TD recognizes the USI.
TD will hash the SI and the hash map will point to the
subtable in one AMP. The subtable row will point the row-id
and the row is fetched from the second amp.

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Hi frinds pls help me regarding this question WHY usi is two amp operation in teradata? THANKS I..

Answer / nitin bansal

Generally the Parsing Engine preapres a two amp plan for
USI, as in case of USI there will be a subtable which has
the hashed value of the USI and the ROW ID of the Primary
Index. So when you search using the USI first it will go to
the AMP which has the subtable and then using the ROW id
from the subtable it will go to the AMP where the actual
row resides.

In a case where the PI and USI value are same it can be a
one amp operation as the HASHED value of oth the PI and USI
will go to the same AMP.

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Hi frinds pls help me regarding this question WHY usi is two amp operation in teradata? THANKS I..

Answer / gowthami

Thanks alot nitin for ur rly.

i would like share 1 interview question which was asked in
ibm.

Q)there are two rows like aa6588fhfhf,gru282vbvv.
Question is howcan we retrive the first number from two
rows.

thanks in advance

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