ASP requests and locking
- From: polastine <noone@xxxxxxxxxxx>
- Date: Mon, 25 Aug 2008 02:58:56 -0700
Hi all -
I'm relatively new to ASP.NET, coming over from the PHP dark side =) So far I'm enjoying working with all this very much, especially the templating system, which is light years beyond anything available with PHP or Perl.
Skip the next few paragraphs if you're not interested in the back story =)
I'm currently writing a web app that is designed to handle a very heavy traffic load - about 3 million requests per day, possibly more. That's about 85 requests per second, give or take.
The app is designed to scale out (cluster) on Server 2008. My characterization tests seem to indicate that I can handle about 40 reqs per second on the servers we use, so I'm going to need two or three boxes for this (obviously not 40 reqs per second every hour of every day, that's just the potential peak load profile).
The requests are stateless, sessions are not turned on and what little information I need about the user is stored in a cookie, so there are no server affinity problems. The database is relatively simple, heavily denormalized and performance is excellent. We also have a fairly comprehensive caching system for repeated coherent reads that works a bit like memcached. All this is working fine right now.
The new wrinkle is as follows. There's a need to have a set of configuration values maintained in each of the webheads. Basically this is just a large associative array, in the form Dictionary<string, string> or whatever. The data this thing contains comes from the database. I have the caching and everything else figured out across the cluster, so that's not the problem.
But I'm finding the ASP.NET request model and how it uses threads a bit confusing so I'm wondering if someone can go through the questions below and answer them:
- ASP.NET uses one thread per HTTP request, correct?
- When using the lock(x) C# idiom, that lock is app domain-wide. So if I'm locking to get at the value of a hashtable in the ASP cache, I'm locking all other requests for this particular app pool until the lock block exits. Correct?
- To follow the above, I assume I do have to lock anything that might be accessed at the same time from two or more concurrent requests?
- When accessing properties of a class that contains only static property accessors, do I need to lock? Assume the class is not accessing anything that is shared internally, just other static variables.
- Assume the class is accessing a hashtable instance declared as a private static variable, but still from a static method. Is the lock necessary? i.e.:
public static class Foo {
private static Hashtable _ht;
...
...
public static int SomeProperty {
get {
// Would not locking here cause a contention problem?
return (int) _ht["SomeProperty"];
}
}
}
It's probably clear by now that I'm trying to figure out how to best store and access these key/value pairs, from a performance perspective. It's also probably clear that I can't afford a lock at all. I also looked at HttpRequest.Items, however that does not help me because I'd have to create (or clone) an instance of the config class for every request, or keep a pool or something complicated like that.
A final question about locking and the ASP cache. If I have a cache item which is a large string (maybe some prebuilt markup for a page that rarely changes), and I access that string from an HTTP request to push it out into the response stream, is the process of pulling that string from the cache a locking situation as well? I.e., does the ASP cache have to lock a primitive type in order to return it? And will this lock affect concurrency at all in heavy load situations?
I realize it's a lot of questions, but even just answering one will help me a lot and maybe set me off on the right path. I'm not having a lot of luck with Google on this. Or if someone has solved this problem before and is willing to share, that would be even better =)
Thanks a lot in advance!
.
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