Session state blocking async ajax call from processed concurrently

Question

I am trying to make 6 asynchronous jQuery ajax calls to my .NET Page Method all at once on document.ready to request for different sets of data from the database and in return render as charts to users.

Problem is that when one chart takes a long time to generate, it locks up generation of the next 5 charts, for instance, when each chart takes 1 min to generate, the user will be approx waiting for 6 mins, instead of 1 - 2 mins which i thought it will be when using async ajax calls and page method gets processed in parallel.

After reading a lot of useful posts in this forum, i found that this is because I have to read and write to session objects within the page methods, and asp.net will lock the whole request, as a result making them run sequentially.

I have seen people suggesting to set the session state to read only in @Page tag, but it will not address my problem because i need write to the session as well. I have considered moving from inProc session to sql database session, but my session object is not serializable and is used across the whole project. I also cannot change to use Cache instead because the session contains user specific details.

Can anyone please help and point me to the right direction? I have been spending days to investigate this page inefficiency and still haven't yet found a nice way yet.

Thanks in advance

Answer 1

From my personal experience, switching to SQL session will NOT help this problem as all of the concurrent threads will block in SQL as the first thread in will hold an exclusive lock on one or more rows in the database.

I'm curious as to why your session object isn't serializable. The only solution that I can think of is use a database table to store the user specific data that you are keeping in session and then only holding onto a database lock for as long as it takes you to update the user data.

You can use the ASP.NET session id or other unique cookie value as the database key.

Answer 2

The problem may not be server side at all.

Browsers have a built in limit on how many concurrent HTTP requests they will make - this is part of the HTTP/1.1 spec which sugests a limit of 2.

In IE7 the limit is 2. in IE8 it is 6. But when a page loads you could easily hit 6 due to the concurrent requests for CSS, JS, images etc.

A good source of info about these limits is BrowserScope (see Connections per Hostname column).

What about combining those 6 requests into 1 request? This will also load a little faster.