Question

I have created a ASMX Web Service which does some Active Directory stuff behind the scene.

As I wish to retain certain information within Web Services under user session, I have decided to put [WebMethod(EnableSession = true)] and start using Session variables.

However, when I turn that option on, the return time from app -> web service -> app has became ridiculously long. (about a minute or more).

If I remove [WebMethod(EnableSession = true)], it is fairly fast.

Anyone know what is going on?

Answer 1

Possible reasons:

1. Session state is stored out of process (state server/ SQL server) and getting/storing it taking a long time
2. You are making multiple concurrent requests (including service requests) under the same session. ASP.NET ensures that only one session-full (session read/write) request execute at a time and hence, multiple concurrent requests would queue up.

EDIT :
For #2, obvious solution is to avoid session state use – for example, can you put the relevant information into another store such as cache or database (expensive).

If you are only reading session state in web service then you may take advantage of read-only session state (see IReadOnlySessionState). Read-only session state allows concurrent read-only requests – read/write request will still block all other requests. Now, EnableSession from WebMethod attribute does not support this – it either provides no session or read/write session. So one of the workaround can be to implement your own handler implementing IReadOnlySessionState and then route asmx request to thi handler using a http-module and then switch the handler to default one later. Because your handler requires read-only session state, you will have the read-only session state – see this forum post where such http-module that switches the handler has been given.