Parallel Language Integrated Query (PLINQ)

text zoom

Parallel Language Integrated Query (PLINQ)

PLINQ is a query execution engine that accepts any LINQ-to-Objects or LINQ-to-XML query and automatically utilizes multiple processors or cores for execution when they are available.

PLINQ Programming Model:

Using PLINQ is almost exactly like using LINQ-to-Objects and LINQ-to-XML. PLINQ supports all of the LINQ operators, not just those available in language comprehensions. And you can query any in-memory collection such as T[], List<T>, or any other kind of IEnumerable<T> in addition to XML documents loaded using the System.Xml.Linq APIs. If you already have a bunch of LINQ queries, PLINQ is equipped to run them.

LINQ-to-SQL and LINQ-to-Entities queries will still be executed by the respective databases and query providers, so PLINQ does not offer a way to parallelize those queries. If you wish to process the results of those queries in memory, including joining the output of many heterogeneous queries, then PLINQ can be quite useful.

Aside from writing LINQ queries the same you can write PLINQ, there are two extra steps needed to make use of PLINQ:

1-Reference the System.Concurrency.dll assembly during compilation.

2-Wrap your data source in an IParallelEnumerable<T> with a call to the System.Linq.ParallelEnumerable.AsParallel extension method.

Calling the AsParallel extension method in Step 2 ensures that the C# or Visual Basic compiler binds to the System.Linq.ParallelEnumerable version of the standard query operators instead of System.Linq.Enumerable. This gives PLINQ a chance to take over control and to execute the query in parallel. AsParallel is defined as taking any IEnumerable<T>:



public static class System.Linq.ParallelEnumerable {

      public static IParallelEnumerable<T> AsParallel<T>(

          this IEnumerable<T> source); 

     ... the other standard query operators ...

  }  



IParallelEnumerable<T> derives from IEnumerable<T> and adds very   little toit, being there simply to facilitate binding 

to PLINQ's ParallelEnumerable query provider