Why PLINQ is giving worse performance then LINQ Query?

Question

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;

How many items are there in collection? What do they look like? — Emond, Apr 01 '15 at 06:36
http://www.albahari.com/threading/part5.aspx - this link you read the guides on the use PLINQ. — sribin, Apr 01 '15 at 11:50

score 3 · Answer 1 · answered Apr 01 '15 at 06:50

3

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.

answered Apr 01 '15 at 06:50

erikkallen

33,800
13
85
120

score 0 · Answer 2 · answered Apr 01 '15 at 06:56

0

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.

answered Apr 01 '15 at 06:56

Steve Drake

1,968
2
19
41

Why PLINQ is giving worse performance then LINQ Query?

2 Answers2