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POWhy is LINQ JOIN so much faster than linking with WHERE?
 

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  1. POWhy is LINQ JOIN so much faster than linking with WHERE?
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    <p>I've recently upgraded to VS 2010 and am playing around with LINQ to Dataset. I have a strong typed dataset for Authorization that is in HttpCache of an ASP.NET WebApplication.</p> <p>So i wanted to know what actually is the fastest way to check if a user is authorized to do something. <a href="https://stackoverflow.com/questions/5518746/how-to-join-with-linq-to-typed-dataset-composite-key-issue">Here</a> is my datamodel and some other informations if somebody is interested.</p> <p>I have checked 3 ways:</p> <ol> <li>direct <strong>database</strong></li> <li>LINQ query with <strong>Where</strong> conditions as "Join" - Syntax</li> <li>LINQ query with <strong>Join</strong> - Syntax</li> </ol> <p>These are the results with 1000 calls on each function:</p> <p><strong>1.Iteration:</strong></p> <ol> <li>4,2841519 sec.</li> <li>115,7796925 sec.</li> <li>2,024749 sec.</li> </ol> <p><strong>2.Iteration:</strong></p> <ol> <li>3,1954857 sec.</li> <li>84,97047 sec.</li> <li>1,5783397 sec.</li> </ol> <p><strong>3.Iteration:</strong></p> <ol> <li>2,7922143 sec.</li> <li>97,8713267 sec.</li> <li>1,8432163 sec.</li> </ol> <p><strong>Average:</strong></p> <ol> <li>Database: 3,4239506333 sec.</li> <li>Where: 99,5404964 sec.</li> <li>Join: 1,815435 sec.</li> </ol> <p>Why is the Join-version so much faster than the where-syntax which makes it useless although as a LINQ newbie it seems to be the most legible. Or have i missed something in my queries?</p> <p>Here are the LINQ queries, i skip the database:</p> <p><strong>Where</strong>: </p> <pre><code>Public Function hasAccessDS_Where(ByVal accessRule As String) As Boolean Dim userID As Guid = DirectCast(Membership.GetUser.ProviderUserKey, Guid) Dim query = From accRule In Authorization.dsAuth.aspnet_AccessRule, _ roleAccRule In Authorization.dsAuth.aspnet_RoleAccessRule, _ role In Authorization.dsAuth.aspnet_Roles, _ userRole In Authorization.dsAuth.aspnet_UsersInRoles _ Where accRule.idAccessRule = roleAccRule.fiAccessRule _ And roleAccRule.fiRole = role.RoleId _ And userRole.RoleId = role.RoleId _ And userRole.UserId = userID And accRule.RuleName.Contains(accessRule) Select accRule.idAccessRule Return query.Any End Function </code></pre> <p><strong>Join:</strong></p> <pre><code>Public Function hasAccessDS_Join(ByVal accessRule As String) As Boolean Dim userID As Guid = DirectCast(Membership.GetUser.ProviderUserKey, Guid) Dim query = From accRule In Authorization.dsAuth.aspnet_AccessRule _ Join roleAccRule In Authorization.dsAuth.aspnet_RoleAccessRule _ On accRule.idAccessRule Equals roleAccRule.fiAccessRule _ Join role In Authorization.dsAuth.aspnet_Roles _ On role.RoleId Equals roleAccRule.fiRole _ Join userRole In Authorization.dsAuth.aspnet_UsersInRoles _ On userRole.RoleId Equals role.RoleId _ Where userRole.UserId = userID And accRule.RuleName.Contains(accessRule) Select accRule.idAccessRule Return query.Any End Function </code></pre> <p>Thank you in advance.</p> <hr> <p><strong>Edit</strong>: after some improvements on both queries to get more meaningful perfomance-values, the advantage of the JOIN is even many times greater than before:</p> <p><strong>Join</strong>:</p> <pre><code>Public Overloads Shared Function hasAccessDS_Join(ByVal userID As Guid, ByVal idAccessRule As Int32) As Boolean Dim query = From accRule In Authorization.dsAuth.aspnet_AccessRule _ Join roleAccRule In Authorization.dsAuth.aspnet_RoleAccessRule _ On accRule.idAccessRule Equals roleAccRule.fiAccessRule _ Join role In Authorization.dsAuth.aspnet_Roles _ On role.RoleId Equals roleAccRule.fiRole _ Join userRole In Authorization.dsAuth.aspnet_UsersInRoles _ On userRole.RoleId Equals role.RoleId _ Where accRule.idAccessRule = idAccessRule And userRole.UserId = userID Select role.RoleId Return query.Any End Function </code></pre> <p><strong>Where</strong>:</p> <pre><code>Public Overloads Shared Function hasAccessDS_Where(ByVal userID As Guid, ByVal idAccessRule As Int32) As Boolean Dim query = From accRule In Authorization.dsAuth.aspnet_AccessRule, _ roleAccRule In Authorization.dsAuth.aspnet_RoleAccessRule, _ role In Authorization.dsAuth.aspnet_Roles, _ userRole In Authorization.dsAuth.aspnet_UsersInRoles _ Where accRule.idAccessRule = roleAccRule.fiAccessRule _ And roleAccRule.fiRole = role.RoleId _ And userRole.RoleId = role.RoleId _ And accRule.idAccessRule = idAccessRule And userRole.UserId = userID Select role.RoleId Return query.Any End Function </code></pre> <h2>Result for 1000 calls (on a faster computer)</h2> <ol> <li>Join | 2. Where</li> </ol> <p><strong>1.Iteration:</strong></p> <ol> <li>0,0713669 sec.</li> <li>12,7395299 sec.</li> </ol> <p><strong>2.Iteration:</strong></p> <ol> <li>0,0492458 sec.</li> <li>12,3885925 sec.</li> </ol> <p><strong>3.Iteration:</strong></p> <ol> <li>0,0501982 sec.</li> <li>13,3474216 sec.</li> </ol> <p><strong>Average:</strong></p> <ol> <li>Join: 0,0569367 sec.</li> <li>Where: 12,8251813 sec.</li> </ol> <hr> <p>Join is 225 times faster </p> <p><strong>Conclusion:</strong> avoid WHERE to specify relations and use JOIN whenever possible(definitely in <a href="http://msdn.microsoft.com/en-us/library/bb386977.aspx" rel="noreferrer">LINQ to DataSet</a> and <code>Linq-To-Objects</code> in general).</p>
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