I just discovered why all ASP Net websites are slow and I am trying to work out what to do about it

Question

I just discovered that every request in an ASP Net web application gets a Session lock at the beginning of a request  and then releases it at the end of the request   In case the implications of this are lost on you  as it was for me at first  this basically means the following    Anytime an ASP Net webpage is taking a long time to load  maybe due to a slow database call or whatever   and the user decides they want to navigate to a different page because they are tired of waiting  THEY CAN T  The ASP Net session lock forces the new page request to wait until the original request has finished its painfully slow load  Arrrgh  Anytime an UpdatePanel is loading slowly  and the user decides to navigate to a different page before the UpdatePanel has finished updating    THEY CAN T  The ASP net session lock forces the new page request to wait until the original request has finished its painfully slow load  Double Arrrgh    So what are the options   So far I have come up with    Implement a Custom SessionStateDataStore  which ASP Net supports   I haven t found too many out there to copy  and it seems kind of high risk and easy to mess up  Keep track of all requests in progress  and if a request comes in from the same user  cancel the original request   Seems kind of extreme  but it would work  I think   Don t use Session   When I need some kind of state for the user  I could just use Cache instead  and key items on the authenticated username  or some such thing  Again seems kind of extreme    I really can t believe that the ASP Net Microsoft team would have left such a huge performance bottleneck in the framework at version 4 0  Am I missing something obvious  How hard would it be to use a ThreadSafe collection for the Session

User · Answer

Just to help anyone with this problem  locking requests when executing another one from the same session      Today I started to solve this issue and  after some hours of research  I solved it  by removing the Session Start method  even if empty  from the Global asax file   This works in all projects I ve tested

User · Answer

I prepared a library based on links posted in this thread  It uses the examples from MSDN and CodeProject  Thanks to James   I also made modifications advised by Joel Mueller   Code is here   https   github com dermeister0 LockFreeSessionState  HashTable module   Install-Package Heavysoft LockFreeSessionState HashTable   ScaleOut StateServer module   Install-Package Heavysoft LockFreeSessionState Soss   Custom module   Install-Package Heavysoft LockFreeSessionState Common   If you want to implement support of Memcached or Redis  install this package  Then inherit the LockFreeSessionStateModule class and implement abstract methods      The code is not tested on production yet  Also need to improve error handling  Exceptions are not caught in current implementation    Some lock-free session providers using Redis    https   github com angieslist AL-Redis  Suggested by gregmac in this thread   https   github com welegan RedisSessionProvider  NuGet  RedisSessionProvider  https   github com efaruk playground tree master UnlockedStateProvider  NuGet  UnlockedStateProvider Redis

User · Answer

OK  so big Props to Joel Muller for all his input  My ultimate solution was to use the Custom SessionStateModule detailed at the end of this MSDN article    http   msdn microsoft com en-us library system web sessionstate sessionstateutility aspx   This was    Very quick to implement  actually seemed easier than going the provider route  Used a lot of the standard ASP Net session handling out of the box  via the SessionStateUtility class    This has made a HUGE difference to the feeling of  snapiness  to our application   I still can t believe the custom implementation of ASP Net Session locks the session for the whole request   This adds such a huge amount of sluggishness to websites   Judging from the amount of online research I had to do  and conversations with several really experienced ASP Net developers   a lot of people have experienced this issue  but very few people have ever got to the bottom of the cause   Maybe I will write a letter to Scott Gu     I hope this helps a few people out there

User · Answer

If your page does not modify any session variables  you can opt out of most of this lock    lt    Page EnableSessionState  ReadOnly    gt    If your page does not read any session variables  you can opt out of this lock entirely  for that page    lt    Page EnableSessionState  False    gt    If none of your pages use session variables  just turn off session state in the web config    lt sessionState mode  Off    gt    I m curious  what do you think  a ThreadSafe collection  would do to become thread-safe  if it doesn t use locks   Edit  I should probably explain by what I mean by  opt out of most of this lock   Any number of read-only-session or no-session pages can be processed for a given session at the same time without blocking each other  However  a read-write-session page can t start processing until all read-only requests have completed  and while it is running it must have exclusive access to that user s session in order to maintain consistency  Locking on individual values wouldn t work  because what if one page changes a set of related values as a group  How would you ensure that other pages running at the same time would get a consistent view of the user s session variables   I would suggest that you try to minimize the modifying of session variables once they have been set  if possible  This would allow you to make the majority of your pages read-only-session pages  increasing the chance that multiple simultaneous requests from the same user would not block each other

User · Answer

If you are using the updated Microsoft Web RedisSessionStateProvider starting from 3 0 2  you can add this to your web config to allow concurrent sessions    lt appSettings gt       lt add key  aspnet AllowConcurrentRequestsPerSession  value  true   gt   lt  appSettings gt    Source

User · Answer

For ASPNET MVC  we did the following    By default  set SessionStateBehavior ReadOnly on all controller s action by overriding DefaultControllerFactory On controller actions that need writing to session state  mark with attribute to set it to SessionStateBehavior Required   Create custom ControllerFactory and override GetControllerSessionBehavior       protected override SessionStateBehavior GetControllerSessionBehavior RequestContext requestContext  Type controllerType                var DefaultSessionStateBehaviour   SessionStateBehaviour ReadOnly           if  controllerType    null              return DefaultSessionStateBehaviour           var isRequireSessionWrite               controllerType GetCustomAttributes lt AcquireSessionLock gt  inherit  true  FirstOrDefault      null           if  isRequireSessionWrite              return SessionStateBehavior Required           var actionName   requestContext RouteData Values  action   ToString            MethodInfo actionMethodInfo           try                       actionMethodInfo   controllerType GetMethod actionName  BindingFlags IgnoreCase   BindingFlags Public   BindingFlags Instance                     catch  AmbiguousMatchException                        var httpRequestTypeAttr   GetHttpRequestTypeAttr requestContext HttpContext Request HttpMethod                actionMethodInfo                   controllerType GetMethods   FirstOrDefault                      mi   gt  mi Name Equals actionName  StringComparison CurrentCultureIgnoreCase   amp  amp  mi GetCustomAttributes httpRequestTypeAttr  false  Length  gt  0                      if  actionMethodInfo    null              return DefaultSessionStateBehaviour           isRequireSessionWrite   actionMethodInfo GetCustomAttributes lt AcquireSessionLock gt  inherit  false  FirstOrDefault      null            return isRequireSessionWrite   SessionStateBehavior Required   DefaultSessionStateBehaviour             private static Type GetHttpRequestTypeAttr string httpMethod                 switch  httpMethod                        case  GET                   return typeof HttpGetAttribute               case  POST                   return typeof HttpPostAttribute               case  PUT                   return typeof HttpPutAttribute               case  DELETE                   return typeof HttpDeleteAttribute               case  HEAD                   return typeof HttpHeadAttribute               case  PATCH                   return typeof HttpPatchAttribute               case  OPTIONS                   return typeof HttpOptionsAttribute                      throw new NotSupportedException  unable to determine http method            AcquireSessionLockAttribute   AttributeUsage AttributeTargets Method   public sealed class AcquireSessionLock   Attribute       Hook up the created controller factory in global asax cs  ControllerBuilder Current SetControllerFactory typeof DefaultReadOnlySessionStateControllerFactory      Now  we can have both read-only and read-write session state in a single Controller   public class TestController   Controller         AcquireSessionLock      public ActionResult WriteSession                 var timeNow   DateTimeOffset UtcNow ToString            Session  key     timeNow          return Json timeNow  JsonRequestBehavior AllowGet              public ActionResult ReadSession                 var timeNow   Session  key            return Json timeNow     empty   JsonRequestBehavior AllowGet                Note  ASPNET session state can still be written to even in readonly   mode and will not throw any form of exception  It just doesn t lock to   guarantee consistency  so we have to be careful to mark AcquireSessionLock in controller s actions that require writing session state

User · Answer

I started using the AngiesList Redis RedisSessionStateModule  which aside from using the  very fast  Redis server  for storage  I m using the windows port -- though there is also an MSOpenTech port   it does absolutely no locking on the session   In my opinion  if your application is structured in a reasonable way  this is not a problem  If you actually need locked  consistent data as part of the session  you should specifically implement a lock concurrency check on your own   MS deciding that every ASP NET session should be locked by default just to handle poor application design is a bad decision  in my opinion  Especially because it seems like most developers didn t don t even realize sessions were locked  let alone that apps apparently need to be structured so you can do read-only session state as much as possible  opt-out  where possible

User · Answer

Marking a controller s session state as readonly or disabled will solve the problem   You can decorate a controller with the following attribute to mark it read-only    SessionState System Web SessionState SessionStateBehavior ReadOnly     the System Web SessionState SessionStateBehavior enum has the following values    Default Disabled ReadOnly Required

User · Answer

After struggling with all available options  I ended up writing a JWT token based SessionStore provider  the session travels inside a cookie  and no backend storage is needed    http   www drupalonwindows com en content token-sessionstate  Advantages    Drop-in replacement  no changes to your code are needed  Scale better than any other centralized store  as no session storage backend is needed  Faster than any other session storage  as no data needs to be retrieved from any session storage Consumes no server resources for session storage  Default non-blocking implementation  concurrent request won t block each other and hold a lock on the session Horizontally scale your application  because the session data travels with the request itself you can have multiple web heads without worrying about session sharing

User · Answer

Unless your application has specially needs  I think you have 2 approaches    Do not use session at all Use session as is and perform fine tuning as joel mentioned    Session is not only thread-safe but also state-safe  in a way that you know that until the current request is completed  every session variable wont change from another active request  In order for this to happen you must ensure that session WILL BE LOCKED until the current request have completed   You can create a session like behavior by many ways  but if it does not lock the current session  it wont be  session    For the specific problems you mentioned I think you should check HttpContext Current Response IsClientConnected  This can be useful to to prevent unnecessary executions and waits on the client  although it cannot solve this problem entirely  as this can be used only by a pooling way and not async

[asp.net] I just discovered why all ASP.Net websites are slow, and I am trying to work out what to do about it

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