PLINQ Queries That Run in Parallel in .NET 4.5

re: PLINQ Queries That Run in Parallel in .NET 4.5

Richard Deeming — Thu, 08 Dec 2011 17:45:46 GMT

I was suggesting that these bugs, and probably many others, should be fixed. If you're willing to risk breaking backwards compatibility to improve performance, I don't understand why you won't risk it to fix something that's broken! :)

The second bug is particularly apposite:

"while well-behaved implementations ... should handle this fine, there may be some implementations ... that are not expecting us to reverse the order in which we supply these arguments for a given list"

A developer writing an IComparer implementation which depends on the precise implementation of the sorting algorithm used internally is protected from breaking changes, whereas someone using PLINQ incorrectly isn't.

re: PLINQ Queries That Run in Parallel in .NET 4.5

Stephen Toub - MSFT — Thu, 08 Dec 2011 17:09:09 GMT

Richard, thank you for the feedback. Are you suggesting we not fix PLINQ's performance, or are you suggesting that those two bugs you link to should also be fixed? It's not clear to me what you're hoping for.

Part of the point with PLINQ is that its up to the heuristics used in PLINQ internally to determine how to execute a particular query, and those heuristics may evolve over time. A developer explicitly opting-in to using PLINQ is doing so because they want their query to run in parallel, and has as such already affirmed it's ok for the system to do so (expected, in fact). That PLINQ then was in some limited circumstances not running those queries in parallel is what was addressed here.

re: PLINQ Queries That Run in Parallel in .NET 4.5

Richard Deeming — Thu, 08 Dec 2011 17:01:01 GMT

So you won't fix bugs like [1] and [2] in case they break some hypothetical code you've never seen, but you'll change the fundamental behaviour of PLINQ without adding an "old behaviour" switch and just hope it doesn't break anything?

[1] connect.microsoft.com/.../colortranslator-fromhtml-throws-a-system-exception

[2] connect.microsoft.com/.../orderbydescending-fails-in-linq-to-objects-when-a-comparer-returns-int-minvalue

re: PLINQ Queries That Run in Parallel in .NET 4.5

Satish — Fri, 02 Dec 2011 07:19:49 GMT

How we acheive Parallel programming with Database?.

For Example We have 10000 records to insert into Database ,We are writng dotnet code to insert records .

From dotnet perspective we are able to acheive .but for data base server will eats up more memory.

Can some suggest how to acheive this.?

re: PLINQ Queries That Run in Parallel in .NET 4.5

Ronald Wildenberg — Fri, 11 Nov 2011 12:56:29 GMT

I was wondering: what are the semantics of First (or FirstOrDefault or Last, etc)? For example, can the following query return 2 instead of 1 (in a better example, 1 and 2 would represent some expensive operation):

(new[] {1, 2}).AsParallel().First();

Or is First order-preserving somehow (and if it is, what's the use of parallelizing it since you simply want to get the first element as fast as possible).