Data is stored based on a selected field(s) that are used for distribution.
==Data (A)==> Hash Function (B) ==> Logical SPU identifier list (C) ==> Physical SPU list (D) ==> Storage (E)
When data arrives, it is hashed based on the field(s) and a hash function (B) is used for this purpose.
For example, for a hypothetical 32 node system, the logical SPU identifier list has 32 unique entries. If there are 1000 hashed data items from (B), there are 1000 entries in (C), all having only 32 SPU entries (a number of data items go to the same SPU, thus multiple (B) entries map to the same (C)). For instance, (C) has values [3,19,30,7,20,25,11,3,22,19….]. This way, 1000 data entries are mapped. (D) has a physical IP address of both primary and failover SPU. If there is a failover, this is the only place where Netezza needs to update its entries. The same goes for a system that has a new SPU added. It is a little complicated, in principle, this is the concept.
