LinqOptimizer

An automatic query optimizer-compiler for Sequential and Parallel LINQ. LinqOptimizer compiles declarative LINQ queries into fast loop-based imperative code. The compiled code has fewer virtual calls and heap allocations, better data locality and speedups of up to 15x (Check the [Performance] (https://github.com/nessos/LinqOptimizer/wiki/Performance) page).

The main idea is that we lift query sources into the world of Expression trees and after various transformations-optimizations we compile them into IL for efficient execution.

var query = (from num in nums.AsQueryExpr() // lift
             where num % 2 == 0
             select num * num).Sum();
             
Console.WriteLine("Result: {0}", query.Run()); // compile and execute

For F# we support functional pipelines and support for F# style LINQ queries is in development.

let query = nums
            |> Query.ofSeq
            |> Query.filter (fun num -> num % 2 = 0)
            |> Query.map (fun num -> num * num)
            |> Query.sum
             
printfn "Result: %d" <| Query.run query // compile and execute

Install via NuGet

Install-Package LinqOptimizer.CSharp
Install-Package LinqOptimizer.FSharp

Optimizations

• Lambda inlining
• Loop fusion
• Nested loop generation
• Anonymous Types-Tuples elimination
• Specialized strategies and algorithms

The expression

var query = (from num in nums.AsQueryExpr()
             where num % 2 == 0
             select num * num).Sum();

will compile to

int sum = 0;
for (int index = 0; index < nums.Length; index++)
{
   int num = nums[index];
   if (num % 2 == 0)
      sum += num * num;
}

and for the parallel case

var query = (from num in nums.AsParallelQueryExpr()
             where num % 2 == 0
             select num * num).Sum();

will compile to a reduce-combine style straregy

Parallel.ReduceCombine(nums, 0, 
                          (acc, num) => { 
                                       if (num % 2 == 0)  
                                         return acc + num * num; 
                                       else
                                         return acc; 
                          }, (left, right) => left + right);

Future work

• Many missing operators
• New specialized operators
• Even more optimizations

References

LinqOptimizer draws heavy inspiration from

• Steno
• Clojure - reducers