Calculate Space Requirements for Hash Tables
Follow these steps to determine the amount of space needed to store the data in a hash table.
1. Create the table and modify it to hash.
2. Determine the number of rows that fit on a page, adjusted for the data page fillfactor to be used.
select tups_per_page * table_dfillpct/100 from iitables where table_name = ‘tablename’;
3. Determine the total number of pages needed for a hash table.
total_hash_pages = (num_rows/(tups_per_page)
Note: Because hashing does not guarantee an equal distribution of rows, the actual number of pages required can be greater than calculated above.