Q:

very large viewstate breaking web app

I have a web app, that consumes a web service. The main page runs a search - by passing parameters to a particular web service method, and I bind the results to a gridview.
I have implemented sorting and paging on the grid. By putting the datatable that the grid is bound to in the viewstate and then reading / sorting / filtering it as necessary - and rebinding to the grid.
As the amount of data coming back from the web service has increased dramatically, when I try to page/sort etc I receive the following errors.
The connection was reset
The connection to the server was reset while the page was loading.
I have searched around a bit, and it seems that a very large viewstate is to blame for this.
But surely the only other option is to 

Limit the results
Stick the datatable in the session rather than the viewstate
Something else I am unaware of

Previously I did have the datatable in the session, as some of this data needed to persist from page to page - (not being posted however so viewstate was not an option). As the amount of data rose and the necessity to persist it was removed, I used the viewstate instead. Thinking this was a better option than the session because of the amount of data the session would have to hold and the number of users using the app.
It appears maybe not.
I thought that when the viewstate got very big, that .net split it over more than one hidden viewstate field, but it seems all I'm getting is one mammoth viewstate that I have trouble viewing in the source.
Can anyone enlighten me as to how to avoid the error I'm getting? If it is indeed to do with the amount of data in the viewstate?

A:

It sounds like your caching the whole dataset for all pages even though you are only presenting one page of that data.  I would change your pagination to only require the data for the current page the user is on.
If the query is heavy and you don't want to have to be constantly calling it over and over because there is a lot of paging back and forth (you should test typical useage pattern) then I would implement some type of caching on the web service end to cache page by page (by specific user if the data is specific to a user) and have it expire rather quick (eg a few minuites).
I think you need to limit the total amount of data your dealing with.  Change your code to not pass back extra data that might never be needed is a good place to start.
EDIT: Based on your comments:

You can't change the web service
The user can manipulate the query by filtering or sorting
There is a large amount of data returned by the web service
The data is user specific

Well I think you have a perfect case for using the Session then.  This can be taxing the the server with large amounts of users and data so you might want to implement some logic to clear the data from the Session and not wait for it to expire (like on certain landing pages you know the user will go when they are done, clear the session data).
You really want to get it out of the ViewState beacuse it is a huge bandwidth hog.  Just look at your physical page size and that data is being passed back and forth with every action.  Moving it to the Session would eliminate that bandwidth useage and allow for you to do everything you need.
You could also look at the data the web service is bringing back and store it in a custom object that you make as 'thin' as possible.  If your storing a DataSet or a DataTable in your Session, those objects have some extra overhead you probably don't need so store the data as an array of some custom thin object and just bind to that.  You would need to map the result from the WS to your custom object but this is a good option you cut down on memory useage.
Let me know if there is something else I am missing.

