Internet Explorer 6 Hangs with Multiple Connections
The code needs to be rewritten no doubt, there are many more efficiencies to be had, but that didn’t explain the hang. I combed over the server, watching response while a user was using the application. The map server stresses the machine, because it needs a ton of I/O and it would spike the CPU frequently, but no processes went to 99% CPU utilization, and the server seemed to respond to other clients even when one of them was hung up. It was pretty clear then that the problem wasn’t with the server. To take this logic a little further, we built a load test using wget and saving the result to a file. We looped over the calls as fast as we could and we never caused the map server to hang. It performed as expected.
The next logical step was to look at the possibility of corrupt files. We did notice that we could get the map server to crash when we fed it corrupt files, but we found no eveidence that the files that we were using in production were corrupt in any way. At this point we were plenty dejected, because we had spent something like 35 hours over a couple days working on this problem and we had nothing. We performed a new ColdFusion install on a different server, we built a server with better hardware, we reinstalled the map server application multiple times, nothing seemed to affect it. We even improved the network bandwidth available to the client, still nothing. At that point I was down to either it was the code, or it was the client.
To test this theory I commented out all of the flash calls on every page and went through the application to try to cause the system to hang. I couldn’t do it, so I had effectively limited the possible cause to the Flash movie. I started to go through what the Flash movie was doing, and what could cause it to fail. The demis people told us that they had seen hangs when the map server wasn’t responding, and the Flash player was parsing XML. This lead me to try the application in Firefox, and lo and behold, it never hung up. It worked like a charm. The only problem was that our client was set on Microsoft Internet Explorer
I started about the arduous task of removing all XML parsing from the Flash code, then I tried it and it still hung. I was truly disappointed, but I rethought what was happening with the XML. It was making server calls, I realized that I could have up to 8 consecutive connections going on. At the time I thought it was nothing, but then I started trying to find out what was different between Internet Explorer and Firefox. I happened upon an article on MSDN about a known bug that Internet Explorer will hang for 5 minutes when there are 2 persistent connections to a server, and rich content is downloaded. I had found my culprit. It turns out that I had to add 2 keys to the registry. MaxConnectionsPerServer, and MaxConnectionsPer1_0Server. I set the latter to 8 and the former to 24, hexadecimal. The keys need to be DWORD keys.
That would allow 8 connections for HTTP 1.0 and 32 or so connections for HTTP 1.1. The HTTP 1.1 guidelines recommend that there only be 2 connections allowed, but if Firefox wasn’t adhering to it, why should I. I added the keys to HKEY_CURRENT_USER>Software>Microsoft>Windows>Current Version>Internet Settings and it worked like a charm. Everything was perfect. Talk about looking for a needle-in-a-haystack. I’m still amazed that I found it.
The purpose of this entry is so that no one has to go through the week that I just went through. Generally no software should be in front of the client before it is ready, but in this case we already had a client. Hopefully this will help anyone out there who is experiencing hangs in Internet Explorer. Darn Microsoft and not fixing bugs for almost 3 years!
*EDIT Make that 8 years, since IE 8 appears to still suffer from the same problem!*
Here are some helpful links that might be better at explaining than I am…