Parallelizing a query with multiple “from” clauses

re: Parallelizing a query with multiple “from” clauses

Keith Patrick — Sat, 08 Dec 2007 00:12:34 GMT

One thing I'm seeing a lot of in the PLINQ samples but I'm not getting is the use of .ToArray(). If Range is returning an Enumerable, what is the difference (outside the extra method and array alloc) between running a select from Array instead of Enumerable?

(sorry if this is explained somewhere right in front of my face, but I've been saturating myself with all things 3.5 the last few days, and I'm sure I'm missing some stuff)

re: Parallelizing a query with multiple “from” clauses

poojanagpal — Sat, 08 Dec 2007 02:03:48 GMT

Good question, Keith.

PLINQ uses the type of the data source to determine the partitioning scheme. For data sources like arrays, lists and IParallelEnumerable.Range, PLINQ can determine the size of the dataset and partition it into "ranges" of pre-calculated lengths. For a data source of type Enumerable, the size cannot be pre-determined. PLINQ uses chunk-partitioning scheme for such datasets. You can read more about Range and Chunk Partitioning at http://blogs.msdn.com/pfxteam/archive/2007/12/02/6558579.aspx

Now, this important is to know while writing PLINQ queries because some applications might perform better with Range partitioning and some with Chunk partitioning.

That said ToArray() in this post is probably confusing since it conflicts with the Ray Tracer code. I will edit the post to make it clear. Thanks for pointing it out!

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