Plinq's Range partitioning vs Chunk partitioning?

Question

In which scenarios Will Range partitioning will be better choice than Chunk partitioning ? (and vise verse)

I already know that

• Chunk partitioning : grabbing smal chunks of elements from the input to process , he starts with small chunks then , increases the chunk size.

• Range partitioning preallocates an equal number of elements to each worker

Also , Why this code : ( finding prime numbers till 100000)

IEnumerable<int> numbers = Enumerable.Range (3, 100000-3);
var parallelQuery =    from n in numbers.AsParallel()
                       where Enumerable.Range (2, (int) Math.Sqrt (n)).All (i => n % i > 0)
                       select n;

Might perform poorly with range partitioning ?

While this code : (finding the sum of sqrt of the first million numbers)

ParallelEnumerable.Range (1, 10000000).Sum (i => Math.Sqrt (i))

Will be better a better choice to use with range partitioning ?

Answer 1

In the first sample , the required tme per item depends on n. Searching for the next prime number after 90000 takes more time than finding the one after 11.

As a result, when divided into equal ranges, the last ranges will have to perform much more work than the first.

In the second sample the time-per-operation is equal over the entire range. So range partitioning will work well.