This is rare these days, because IIS request threads almost never block. IIS hangs happen when all available IIS threads are blocked, causing IIS to stop dequeueing additional requests. Once you confirm the hang, the next step is to determine where its taking place. Struggling with debugging hangs on your own? Learn more about resolving hangs quickly with LeanSentry's automatic hang diagnostics. and then confirms a likely hang with executing request snapshots and the debugger. With LeanSentry, we solved this problem by using progressive hang detection, which starts out with lightweight monitoring of more than a dozen different performance counters. NET queueing counters), and the reliable ones (executing requests, thread snapshots) are prohibitively expensive to monitor all the time. Most of these signs are unreliable on their own (e.g. There are many possible places where a hang can happen, and many possible signs of hangs. While you can almost always tell when you have a hang by requesting your website externally, detecting it internally can be surprisingly hard. If you DO NOT see requests accumulating, its likely that you have slow requests to some parts of your application, but you do not have a hang.ĭetecting a hang reliably is suprisingly difficult. If you see multiple requests that are taking a long time to execute AND you are seeing more and more requests begin to accumulate, you likely have a hang. I recommend an elapsed filter of at least 5 seconds or longer. This will show you which requests are executing, optionally longer than the elapsed filter you specified. %windir%\system32\inetsrv\appcmd list requests /elapsed:10000 You can also automate this by using the AppCmd command line tool: You can view all currently executing requests in InetMgr, by opening the server node, going to Worker Processes, and picking your application pool's worker process: Most importantly, this can also tell you which URLs are causing the hang, and which requests are queued. which will always lead to higher latencies and request queueing. If the number of currently executing requests is growing, this can reliably tell you that requests are piling up. And the best way to detect a hang is: snapshotting currently executing requests.This basically implies that more requests are coming into the system than are being processed, and this always eventually results in queueing. "Http Service Request Queues\ArrivalRate" counter exceeds the "W3WP_W3SVC\Requests / sec" counter for the application pool's worker process over a period of time.This means IIS is falling behind in request processing, so all incoming requests are waiting at least this long to begin getting processed. "Http Service Request Queues\MaxQueueItemAge" performance counter increasing.Here are 3 "reasonable" early detection signs: This is not generally a true hang, but rather just a performance problem with a specific part of your application. Only specific URLs in your application are slow.
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This usually occurs before a full hang develops, but may also represent a stable state for an application that is overloaded. Most requests are slow, but eventually load. In rare cases, you may also get a "high CPU hang", which we don't cover here. Also, most of the time, high CPU does not itself cause a hang. NOTE: Most hangs do not involve high CPU, and are often called "low CPU hangs". Symptoms include detectable request queueing, and sometimes 503 Service Unavailable errors when queue limits are reached. All requests to your application are very slow or time out. Its important to differentiate the following kinds of hangs: It's generally caused by all available application threads becoming blocked, causing subsequent requests to get queued (or sometimes by the number of active requests exceeding configured concurrency limits). You'll need basic knowledge of Microsoft troubleshooting tools, and time.įirst, lets define what website hang really means.Īn IIS website hangs whenever it appears to stop serving incoming requests, with requests either taking a very long time or timing out. In this article, I'll show you how you can systematically isolate and diagnose most hangs in production. They can be caused by complex and interrelated factors that can be difficult to isolate.They may be happening only sometimes and can be hard to catch.Hangs are fairly common for production applications, and can be incredibly frustrating to troubleshoot. Catch and diagnose hangs automatically.Īll of a sudden, your website appears to have stopped working.Note: This is the original guide that inspired LeanSentry's own automatic hang diagnostics.
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