initial size for a Java hash table (HashMap, HashSet, etc.) given an expected
maximum number of elements. The optimum size is the smallest size that's
guaranteed not to result in any rehash / table-resize operations.
Example Usage:
Map<String, Object> hash = new HashMap<String, Object>(Utils.optimumHashSize(expectedMaxElements));
I think we're paying way too heavy a price in unnecessary rehash operations across
the GATK. If you don't specify an initial size, you get a table of size 16 that gets
completely rehashed and doubles in size every time it becomes 75% full. This means you
do at least twice as much work as you need to in order to populate your table:
(n + n/2 + n/4 + ... 16 ~= (1 + 1/2 + 1/4...) * n ~= 2 * n
Mark DePristo
David Roazen