What does the line “hash reduces the key space to a size that can be listed” mean?
I read this as a part of composite partitioning.
Also how hash+list can be considered as composite partitioning?
Could you illustrate these with examples please?
Thanks!
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The basic idea of composite partitioning is that we will first partitioning the table and then each partition will be sub-partitioned. In case of hash+list, we will first partition the table by hashing and then subpartition each partition by list. For example, suppose you are creating a table to store all addresses in india. You can do hashing (though i am not sure which DBMS would allow you to provide own hashing function) and say each postal code results in a number between 0 and 9. For example postal code of Delhi would fall in hash code 0 and hence partition_0. But the same can happen for postal code of Kolkata. In this case, you further do a sub-partition with list and assign delhi postal code to DELHI and Kolkata to KOL via list.
hope i made sense.
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