CODEWITHSUNDEEP
c#plinq
Hakoo Desai
Hakoo Desai

Reputation: 341

Why PLINQ is giving worse performance then LINQ Query?

I am trying to understand PLINQ. So for that,I am querying database which has 102915 products in it.

But shockingly I am seeing that PLINQ takes 18 secs where normal query takes only 4 secs. To understand, I have read this article, PLINQ Performs Worse Than Usual LINQ. But still, I couldn't understand why this took so many secs.

To remove over head, I removed .order(m.sku) in PLINQ, but still it gives same result. Here, is a code for LINQ and PLINQ version.

PLINQ Version

                shootersEntities model = new shootersEntities();
                var IsOnline = cBOnline.Checked;
                var IsDeleted = cBDeleted.Checked;

                Stopwatch s = new Stopwatch();
                s.Start();
                var p = from m in model.products.AsParallel()
                        where ((m.productOnline == IsOnline) || (m.deleted == IsDeleted)) 

                        select new { m.sku, m.productCode, m.quantity };

                var list = p.ToList();
                s.Stop();
                MessageBox.Show((s.ElapsedMilliseconds / 1000).ToString());

                dataGridView1.DataSource = list;

LINQ Version 

                    shootersEntities model = new shootersEntities();
                    var IsOnline = cBOnline.Checked;
                    var IsDeleted = cBDeleted.Checked;

                    Stopwatch s = new Stopwatch();
                    s.Start();


                var p = from m in model.products
                        where ((m.productOnline == IsOnline) || (m.deleted == IsDeleted)) 
                        select new { m.sku, m.productCode, m.quantity };

                var list = p.ToList();
                s.Stop();
                MessageBox.Show((s.ElapsedMilliseconds / 1000).ToString());

                dataGridView1.DataSource = list;

Upvotes: 0

Views: 241

Answers (2)

Steve Drake
Steve Drake

Reputation: 2048

You are filtering after your AsParallel. So you are reading all the rows spinning threads and filtering.

You can confirm this with a sql profile.

Upvotes: 0

erikkallen
erikkallen

Reputation: 34391

Probably because the LINQ version translates the query to SQL (which may or may not be run in parallell on the server) while the PLINQ version needs to retrieve everything from the database and then run filtering and sorting itself.

Upvotes: 3

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