Max streaming connections per session error

Question

I have a flex application that uses messaging with a streaming AMF connection, falling back to polling. When the max number of streaming connections on the server is reached, it does fall back to polling (at least it prints the max-streaming-clients error but the client connects, so I assume it is falling back - how can I tell?). However, occasionally the streaming connection will not initialize and it does not fall back - no messages are received on the client. The following error is logged on the server:
[EMST]09/25/2008 13:43:18.231 [ERROR] Endpoint with id 'my-streaming-amf' cannot grant streaming connection to FlexClient with id 'D5B8E3A1-1A1C-063E-84A6-6A743A1E4EE0' because max-streaming-connections-per-session limit of '1' has been reached.
This would make sense if the issue was caused by trying to initialize the streaming connection in two tabs of a browser, but I am only trying to initialize in one tab. Closing the browser (and thus destroying the session) does not fix it. The only solution I've found is to reboot the client machine. This has happened in both FireFox 3.0.2 and IE 7.
(1) What could cause the client to get in this state?
(2) When it happens, why doesn't it fall back to polling? Is the fallback only for when the server max connections is reached? When the streaming connection doesn't initialize, no messages are received.
(3) Is there a way to explicitly close the streaming connection on the client so we can fix this without rebooting?
Thanks!

Answer 1

Hi Mary. If you turn on Debug level logging on the client and the server you should be able to tell if you have fallen back to a polling channel after the attempt to connect over the streaming channel has been rejected. In the client log, you will see the flex application sending poll requests to the server at the polling interval configured in the channel and in the server log you should see that the server is receiving these requests.
The behaviour you are seeing seems very strange to me. The reason we have the max-streaming-connections-per-session limit on the server is because most browsers limit the number of active connections that can be made to a server from a single session. In IE for example, this is 2. What happens in most cases when the browser's connection limit is reached is that new connections are put on hold until one of the existing connections closes. This would cause your flex application to hang with no errors being reported on the client or the server. This is why we need the max-streaming-connections-per-session setting on the server. This prevents more than one persistent connection from being made from the same session, so the browser should never reach it's max connections per server limit and lock up.
It looks like you are somehow getting the browser to lock up even though the server is only limiting you to one streaming connection per session. It may be possible to do this if you reload the flex application in the browser (by doing a page refresh) in which case the browser could possibly briefly leave the streaming connection open in the background and when you tried to create a new streaming connection, the browser's connection limit to the server would have been reached and the application could hang. When the application hangs are you reloading the swf/page in the browser?
I really don't know why closing the browser wouldn't fix the problem. You're right that closing the browser should end the session. If you launch a new browser and load the swf do you get the same "cannot grant streaming connection" error on the server or is the browser just locked up, ie. no error is received on the client and the server?
You're not using a proxy server or anything like that are you that might be holding a connection open to the server?
-Alex