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Best practice with a schedule/queue service?

I am currently working on a project, this project is basically a web site which as its main function, runs a long calculation task (this task is made up of between 1-10 sub tasks) - (takes about 30-40 seconds to complete on average) and returns a result to the user, as it stands the code uses multiple threading in the site itself (which i don't really like the idea of), so the site continues to run after a button click, whilst this thread in the background continues the calculation.
I'd ideally like to move this calculation into a separate service, to stop the issues related to running threading in a web app. My idea is that it should be a separate service that runs every X seconds to see if any jobs are present in the database, if there are, run them, but i have little experience in writing a reoccurring windows service, and was wondering if anyone has any ideas on the matter, is this the right way to go about such a task, does anyone have any experience of doing something similar, and can anybody recommend any particular ways I should proceed?

I am working on a similar project. I was thinking about create a service, like you, but I didn't see the benefits in my case. I have to do some long calculations, and put it in the cache. I don't know if this is the best practice but what I did was to create a timer on global.asax, perform my calculations and put it into cache. When the request comes I give the last cached value.
I hope this help you.

In a situation like this I always prefer to create a tcp listener that accepts the requests from the clients. If I am using .net, my first choice would be wcf service with tcp or named pipe binding. Then when I receive a request, I start a thread to proceed the request. When the long running process finally ends, I return a callback to the client, which was a url that specified in the first request to the scheduler. IMHO this is the best way to do it.
However you may want to build your application on a proven framework like NServiceBus, RhinoBus, etc. You may implement the same business over them too.

running timer from global.asax vs quartz.net

I am developing a asp.net site that needs hit a few social media sites daily for blanket friend/follower data. I have chosen arvixe business class as my hosting. In the future if we grow, I'd love to get onto a dedicated server and run a windows service, however since that is not in the cards at this point I need another reliable way of running scheduled tasks. I am familiar with running a thread timer from the app_code(global.aspx). However the app pool recycling will cause some problems with the timer. I have never used task scheduling like quartz but have read a lot about it on stackoverflow. I was looking for some advise as to how to approach my goal. One big problem I have using either method is that I will need the crawler threads to sleep for up to an hour regularly due to api call limits. My first thoughts were to use the db to save the starting and ending of a job. When the app pool recycles I would clear out any parts not completed and only start parts that do not have a record of running on that day. What do the experts here think? any good links to sample architecture of this type of scheduling?

It doesn't really matter what method you use, whether you roll your own or use Quartz. You are at the mercy of ASP.NET/IIS because that's where you want to host it.
Do you have a spare computer laying around that can just run a scheduled task and upload data to a hosted database? To be honest, it's possibly safer (depending on your use case) to just do it that way then try to run a scheduler in ASP.NET.

Somewhat along the lines of Bryan's post;
Find a spare computer.
Instead of allowing DB access have it call up a web service on your site. This service call should be the initiator of the process you are trying to do. Don't try to put params into it, just something like "StartProcess()" should work fine.
As far as going to sleep and resuming later take a look at Workflow Foundation. There are some nice built in features to persist state.
Don't expose your DB to the outside world, instead expose that page or web service and wraps some security around that. WCF has some nice built in security features for that.
The best part is when you decide to move off, you can keep your web service and have it called from a Windows Service in the same manner.

As long as you use a persistent job store (like a database) and you write and schedule your jobs so that they can handle things like being killed half way through, having IIS recycle your process is not that big a deal.
The bigger issue is that IIS shuts your site down if it doesn't have traffic. If you can keep your site up, then just make sure you set the misfire policy appropriately and that your jobs store any state data needed to pick up where they left off, you should be able to pull it off.

If you are language-agnostic and don't mind writing your "job-activation-script" in your favourite, Linux-supported language...
One solution that has worked very well for me is:
Getting relatively cheap, stable Linux hosting(from reputable
companies),
Creating a WCF service on your .Net hosted platform that will contain the logic you want to run regularly (RESTfully or SOAP or XMLRPC... whichever suits you),
Handling the calls through your Linux hosted cron jobs, written in your language of choice(I use PHP).
Working very well, like I said. No VPS expense,configurable and externally activated. I have one central place where my jobs are activated, with 99 to 100% uptime(never had any failures).

How to do something periodically in ASP.NET/WCF?

First of all sorry of asking such a dumb question, I am quite a newbie in asp.net.
So, I am supposed to do something periodically, say I am owner of site heartpatients.com (hypothetically) and I want that for each of my site user who visits the site, a message to be shown after 2hrs "Take your pills". so, basically this is all my question, how am I supposed to show this message after every 2hr (or 4, 6 whatever time)after, also how can I customize time.
One more thing, say if I have this method in a WCF service, that shows this message, how can I call that service at a particular time, and that even configured by user (say someone is taking pills after 10hrs?) So how to call that service (that particular method in service) after the time specified by user passes periodically?
I hope I made my question quite clear.
Any help is appreciated.

ASP.NET generally isn't suited as a task scheduler. The nature of the web is as a request/response system. So a web application should just sit and wait for a request, generate a response, and be done.
For any kind of back-end scheduled task, I'd recommend either:
A Windows Service
A console application scheduled to run (I think Windows comes with a task scheduler)
There are pros and cons either way. For example, a Windows Service will run from boot time and has no console UI, and is generally very manageable from a server perspective. While a console application is traditionally simpler to write and debug.
These can still share code from your web application. If your business logic and data access and all that good stuff are in their own projects/assemblies then these other applications can use those assemblies just as well. (Of course, if everything in your web application is UI-bound, that's another question entirely.)
What concerns me the most is... How do you plan to show this message to a user? Is the user just sitting on your website for hours at a time and you need to remind them to take their meds? Or do you plan to send an email or something? Maybe the example you gave doesn't really explain what you're trying to do? I'm not sure.
Running tasks in the background is one thing, but it seems to me that an entire half of your overall equation (displaying a message to the user) is sort of glazed over and not really thought through.

Check out Quartz.Net: http://quartznet.sourceforge.net/
It enables you to schedule tasks to run using cron expressions:
http://en.wikipedia.org/wiki/Cron

How should I complete this type of notification?

I am basically creating a site for recruiters. One of the functionality in my application requires posting to Facebook periodically. The posting frequency can be from 0(Never) to 4(High)
For Eg. If a recruiter has 4 open jobs and he has posting frequency set to 4, each job should be posted as per it's turn: 1st job on 1st day, 2nd job on 2nd, 3rd job on 3rd etc, on 5th day again 1st job (round robin fashion).
Had he set the posting frequency to 2, two jobs would be posted daily (thus each job would be posted every 2 days)
My only question is what type of threading should I create for this since this is all dynamic!! Also, any guidelines on what type of information should I store in database?
I need just a general strategy to solve this problem. No code..

I think you need to seperate it from your website, I mean its better to run the logic for posting jobs in a service hosted on IIS ( I am not sure such a thing exists or not, but I guess there is).
Also you need to have table for job queue to remember which jobs need to be posted, then your service would pick them up and post them one by one.
To decide if this is the time for posting a job you can define a timer with a configurable interval to check if there is any job to post or not.
Make sure that you keep the verbose log details if posting fails. It is important because it is possible that Facebook changes its API or your API key becomes invalid or anything else then you need to know what happened.
Also I strongly suggest to have a webpage for reporting the status of jobs-to-post queue, if they failed what was the causes of problem.

If you program runs non-stop, you can just use one of the Timer classes available in .NET framework, without the need to go for full-blown concurrency (e.g. via Task Parallel Library).
I suspect, though, that you'll need more than that - some kind of mechanism to detect which jobs were successfully posted and which were "missed" due program not running (or network problems etc.), so they can be posted the next time the program is started (or network becomes available). A small local database (such as SQLite or MS SQL Server Compact) should serve this purpose nicely.

If the requirements are as simple as you described, then I wouldn't use threading at all. It wouldn't even need to be a long-running app. I'd create a simple app that would just try to post a job and then exit immediately. However, I would scheduled it to run once every given period (via Windows Task Scheduler).
This app would check first if it hasn't posted any job yet for the given posting frequency. Maybe put a "Last-Successful-Post-Time" setting in your datastore. If it's allowed to post, the app would just query the highest priority job and then post it to Facebook. Once it successfully posts to Facebook, that job would then be downgraded to the lowest priority.
The job priority could just be a simple integer column in your data store. Lower values mean higher priorities.
Edit:
I guess what I'm suggesting is if you have clear boundaries in your requirements, I would suggest breaking your project into multiple applications. This way there is a separation of concerns. You wouldn't then need to worry how to spawn your Facebook notification process inside your web site code.

Need advice to query data from sql server on every 5 seconds and send it to other app.(.NET C#)

I have a require ment to read data from a table(SQL 2005) and send that data to other application for every 5 seconds. I am looking for the best approach to do the same.
Right now I am planning to write a console application(.NET and C#) which will read the data from sql server 2005(QUEUE table which will be filled through different applications) and send to other application through TCP/IP(Central server). Run that console application under schedule task for every 5 seconds. I am assuming scheduled task will take care to discard new run event if task is already running(avoid to run concurrent executions).
Does any body come accross similar situation? Please share your experience and advice me for best approach.
Thanks in advance for your valuable time spending for my request.
-Por-hills-

We have done simliar work. If you are going to query a sql database every 5 seconds, be sure to use a stored procedure that is optimized to be very fast. It should not update data unless aboslutely necessary. This approach is typically called 'polling' and I've found that it is acceptable if your sqlserver is not otherwise bogged down with too many other calls.
In approaches we've used, a Windows Service that does the polling works well.
To communicate results to another app, it all depends on what your other app is doing and what type of interface you can make into it, and how quickly you need the results. The WCF class libraries from Microsoft provide many workable approaches for real time communication. My preference is to write to the applications database, and then have the application read the data (if it works for that app). If you need something real time, WCF is the way to go, and I'd suggest using a stateless protocol like http if < 5 sec response time is required, (using standard HTTP posts), or TCP/IP if subsecond response time is required.

since I assume your central storage is also SQL 2005, have you considered using what SQL Server 2005 offers out of the box to achieve your requirements? Rather than pool every 5 seconds, marshal and unmarshal TCP/IP, implement authentication and authorization for the TCP/IP pipe, scale TCP transmission with boxcaring, manage message acknowledgments and retries, deal with central site availability, fragment large messages, implement fairness in transmission and so on and so forth, why not simply use Service Broker? It does all you need and more, out of the box, already tested, already tuned for performance and scalability.
Getting reliable messaging right is not trivial and you should focus your efforts in meeting your business specifics, not reiventing the wheel.

I would recommend writing a Windows Service (since you are C#) that has some timer which runs every 5 seconds. That way you wont be starting and stopping an application all the time, it can run even when there is no one logged into the machine, and it will automatically start when the machine is restarted.

For one of my projects, I needed to do something periodically. I opted for a service and set up a timer that takes care of reading the data. You might consider that solution. It has worked well for me.

I suggest to create a windows service and not an application and to perform the timing yourself - create a timer and execute one step on each timer event. For the communication you have many choices - I would consider using standard technologies like a webservice or Winows Communication Foundation.
Besides this custom solution I would evaluate if the task can be solved using Microsoft Integration Services .
Finally other question comes to mind - why do you need this application? Why doesn't/don't the application(s) consuming the data query the database? Is the expensive polling required? Is it possible for the data producers to signal the availibilty of new data directly to the data consumers?

I am not sure about the details of your project, specifically related to security but maybe it would be better to create an SSIS package and schedule it as a job?