I am developing a website using Ruby on Rails and I am doing a bit of rough planning. I can and have deployed rails websites before, just adding to the database and retrieving from database based on my use case, but this time around, its a bit different. I am adding to database but i will need the data to be processed on the server before the data is being sent back to the user or when he decides to retrieve it. What i do not get is how i am going to process the data on the server. I know this doesnt follow the normal pattern for asking questions, i would search for it with google except I dont know what I am looking for. A nudge in the right direction will do.
What I want to do exactly is have users register and click a button (request) which puts the users id in an array , what I need to do on the server is to randomly or not randomly connect two users based on some qualities, this program keeps running infinitely, such that the user can come back later to check if he has been connected with someone already.
This kind of logic typically belongs in the controller, or perhaps on the models. You should read the Rails docs, particularly on controllers: http://guides.rubyonrails.org/action_controller_overview.html
I think you may find a lot of benefit from running a background job for this that is constantly looking for matches. You could have an infinitely running Sidekiq process that is queued up with users. Then once one finishes, just fire it up again.
Or you could create a rake task that does a User.find_each and have it run again when the task finishes. But this would make things blocking if you end up having a lot of users. I'd recommend one job per user and just bloat the system with them. This way you can scale out both horizontally and vertically.
You'll want to learn about ActiveJob and Sidekiq to help achieve what you're looking for :). Sidekiq requires Redis which you'll also have to setup as well. I'd recommend the redis-rails gem to help with the integration.
To go off BenMorganIO's answer, I think this is a job for a background worker. This is a job that is processed in the background, so it doesn't slow up your app. A good example of this is firing off an email in the background.
There are primarily 3 gems I've seen for this:
delayed_job
Resque
Sidekiq (just celebrated 5 years!)
Those should point you in the right direction.
we are currently developing a chat (like facebook, with stored messages).
at the moment, theres a minimum of 500 online users (its a dating website) and at the peak there is a max of 3000 users simultanously online.
switching to websockets is "the thing" for us, but while using the gem "websocket-rails" we fear a little the performance.reading articles like https://www.igvita.com/2008/11/13/concurrency-is-a-myth-in-ruby/ is causing some doubts.
so our question is:
does websocket-rails is killing our application or not? the other choice would be running a jsnode server and switch to faye which shouldnt be a problem in our scalabitliy. does somebody is having any expereince with the scalability of websocket-rails?
The GIL is still here, but should not be the main issue. The main problem is that the Rails approach does not fit well in a massive chat approach.
My suggestion is to switch to event machine for this specific part, and still use websocket (or others push mechanism, like pusher), and use this kind of WebSocket EventMachine Client.
You will be then event driven, with a single ruby thread and you still can use all the others rails existing libraries (that's the node.js model)
I am writing a Rails app that "scrapes/navigates" some other websites and webservices for content. I am using Mechanize and Savon to do the heavylifting.
But given the dynamic nature of the web, I'd like to make my calls to these editable by the admin users of the site - rather than requiring me to release a new version of the site.
The actual scraping thread happens async to the website, using the daemons gem.
My requirements are:
Thinking that the scraping/webservice calling code is quite simple, the easiest route is to make the whole class editable by the admins.
Keep a history of the scraping code - so that we can fairly easily revert if we introduce a problem.
Initially use the code from the file system, but as soon as thats been edited and stored somewhere, to use that code instead.
I am thinking my options are:
Store the code in the db (with a history table for the old versions)
Store the code in a private git repo somewhere and access that for the history/latest versions.
I am thinking the git route might be easiest, given its raison d'etre is to track file history...
But perhaps there is a gem/plugin that does all this for me, out of the box?
Thanks in advance for any tips/advice.
~chris
I really hope you aren't doing something like what's talked about here...
Assuming you are doing a proper mixin, there used to be a gem called "acts_as_versioned" which would do something like you want. It's been a while so I don't know if it's been turned into a plugin or if it's been abandoned. Essentially the process it uses was to provide a combination key for your versioned table.
Your database would have a structure like this:
Key column (id for the record)
Version column (id for the record's version)
All the record attributes
Let's say you had a table for your scripts, and the script you wanted has three versions. Your table would have the following records:
123, 3, '#Be good now'
123, 2, 'puts "Hi"'
123, 1, '#Do not be bad'
Getting the most recent version would be as simple as
Scripts.find :first, :conditions=>{:id=>123}, :order=>"version desc"
Rolling back would be as simple as removing the most recent version, or having another table with a pointer to the active version. It's up to you.
You are correct in that git, subversion, mercurial and company are going to be much better at this. To provide support, you just follow these steps:
Check out the script on the server (using a tag so you can manage what goes there at any time)
Set up a cron job to check out the new script periodically (like every six hours or whatever you feel comfortable with)
The daemon you have for running the script should run the new version automatically.
IF your site is already under source control, and IF you're running under mod_rails/passenger, you could follow this procedure:
edit scraping code
commit change locally
touch yourapp/tmp/restart.txt
that should give you history of the change and you shouldn't have to re-deploy.
A bit safer, but not sure if it's possible for you is on a test/developement server: make change, commit locally, test it, then on production server, git pull then touch tmp/restart.txt
I've written some big spiders and page analyzers in the past, and one of the things to keep in mind is what code is providing what service to the entire application.
Rails is providing the presentation of the data being gathered by your spidering engine. The presentation is one side of the coin, and spidering is the other, and they should be two separate code bases, tied together by some data-sharing mechanism, which, in your case, is the database. The database gives you some huge advantages as does having Rails available, when your spidering code is separate. It sounds like you have some separation already, but I'd recommend creating a wider gap. With that in mind, here's how I've done it before, and what I'd do now.
Previously, I had a separate app for my spidering that was spawning multiple spider tasks. Each task would look at a bunch of different URLs, throw their results in the database, then quit. Each time one quit the main app would spawn another spider to process more URLs. Each loop, the main app checked a YAML configuration file for run-time parameters, like how many sub-tasks it should have running, how many URLs they'd get, how long they'd wait for connections, etc. It stored the last modification date of the config file each time it loaded it so, if I made a change to the file, the app would sense it in a reasonably short time, reread the file, and adjust its behavior.
All state information about the URLs/pages/sites being scraped/spidered, was kept in the database so I could check on its progress. I could see how many had been processed or remained in the queue, the various result codes, and the content being returned. If I didn't like something I could even tweak the filters to skip junk pages, knowing the spidering tasks would be updated in a few minutes.
That system worked extremely well, spidered a major customer's series of websites without a glitch, running for several weeks as I added new sites to the list. (We were helping one of the Fortune 50 companies improve their sites, and every site had been designed and implemented by a different team, making every site completely different. My code had to be flexible and robust; I was really happy with how it worked out.)
To change it, these days I'd use a database table to hold all the configuration info. That way I could easily build an admin form, and let someone else inherit the task of adjusting the app's runtime configuration. The spider tasks would also be written so they'd pull their configuration from the database, rather than inherit it from the main app. I originally had the main app do all the administration and pass the config info to the spidering apps because I wanted to keep the number of connections to the database as low as possible. I was using Postgres and now know it could have easily handled the load, so by letting the individual tasks handle their configuration I could have made it more responsive.
By making the spidering engine separate from the presentation engine it was possible to temporarily stop one or the other without affecting the progress of the spidering job. Once I had the auto-reload of the prefs in place I don't think I had to stop the spidering engine, I just adjusted its prefs. It literally ran for weeks without stopping and we eventually pulled the plug because we had enough data for our needs.
So, I'd recommend tweaking your code so your spidering engine doesn't rely on Rails, instead it will be fired off by cron or a separate scheduling app. If you have to temporarily stop Rails your engine will run anyway. If you have to temporarily stop the engine then Rails can continue serving pages. The database sits between the two acting as the glue.
Of course, if the database goes down you're hosed all the way around, but what else is new? :-)
EDIT: Chris said:
"I see your point about the splitting the code out, though my Ruby-fu is low - not sure how far I can separate things without having to have copies of the ActiveModel/migrations stuff, plus some shared model classes."
If we look at your application as spider engine <--> | <-- database --> | <--> Rails/MVC/presentation, where the engine and Rails separately read and write to the database, and look at what each does well, that helps figure out how to break them into separate code bases.
Rails is designed to handle migrations, so let it. There's no reason to reinvent that wheel. But, how often do you do migrations, and what is effected when you do? You do them seldom once the application is stable, and, at that point you'd do them in a maintenance cycle to tweak the database. You can shut down the spidering engine and the web interface for a few minutes, migrate the database, then bring things up and you're off and running. Migrations are a necessary evil, but are hardly show-stoppers once in production. Most enterprises have "Software Sunday", or some pre-announced window of maintenance, so do the same.
ActiveRecord, modeling and associations are pretty easy to deal with too. The models are in a file that is required internally by Rails already, so the spidering engine can inherit the database know-how that way too; Multiple apps/scripts can use the same model file. You don't see the Rails books talk about it much, but ActiveRecord is actually pretty easy to use outside of Rails. Search the googles for activerecord without rails for more info.
You can pull in ActiveSupport also if you want some of its extensions to classes by doing a regular require, but the Rails "view" and "controller" logic, which normally applies to presenting the web interface, shouldn't be needed at all in the engine.
Business logic, which goes in the controllers in Rails could even be refactored into separate methods that get required by the Rails side of things and by the spidering engine. It's a different way of looking at Rails but falls in line with the "DRY" mantra - don't repeat yourself, so make things modular and require (or require_relative) bits and pieces that are the building blocks of the entire system.
If you don't want a totally separate codebase, you can take advantage of Rail's script runner, which gives a script access to the ActiveRecord::Base and ActiveRecord::Associations and ActiveSupport. Do a rails runner -h from your app's main directory, or search for "rails runner" for more info. runner is not good for a job that starts and runs many times an hour, because Rail's startup cost is high. But, if you have a long-running task, say one that runs in parallel with your rails app, then it's a great choice. I'd give it serious consideration for the spidering side of your application. Eventually you might want to break the spidering-engine out to a separate host so the presentation side has a dedicated host, so runner will help you buy time and do it in small steps.
I need to display logfiles in real time to user webpage using ruby/rails. Users should be able to see logfile steaming without refreshing the page.
Logfiles may not always be in the same machine which runs rails.
Is it possible in ruby/rails ?.
You could do this with automatically refreshing page, using AJAX when JavaScript is available (this avoids page flicker and extra bandwidth usage caused by a page reload).
The other approach (actually incrementally updating page) consists of two separate issues: (1) reading the file as it grows, and (2) sending the answer without closing the connection. I have seen some solutions doing this (not in Rails, though), but unfortunately they tend not to be very reliable (browsers and other parts of the system will timeout) and the users get confused when the page loading never finishes.
Ruby and Rails can read files, but the issue is going to be accessing from different machines. Are the logfiles on the same network?
What you're asking for is not necessarily Rails-specific. It's more a question of technology, IMO.
Because the classic web model is client/server and pushing data asynchronously is not standard, you'll need to figure out how to do it either by:
1) faking it by polling on the client.
2) use a different technology. For Rails, you may want to look into something like comet or websockets.
I've been sending emails on my application (ruby 1.8.7, rails 2.3.2) like this
Thread.new{UserMailer.deliver_signup_notification(user)}
Since ruby use green threads, there's any performance advantage doing this, or I can just use
UserMailer.deliver_signup_notification(user)
?
Thanks
Global VM lock will still almost certainly apply while sending that email, meaning no difference.
You should not start threads in a request/response cycle. You should not start threads at all unless you can watch them from create to join, and even then, it is rarely worth the trouble it creates.
Rails is not thread-safe, and is not meant to be from within your controller actions. Only since Rails 2.3 has just dispatching been thread-safe, and only if you turn it on in environment.rb with config.threadsafe!.
This article explains in more detail. If you want to send your message asynchronously use BackgroundRb or its analog.
In general, using green threads to run background tasks asynchronously will mean that your application can respond to the user before the mail is sent. You're not concerned about exploiting multiple CPUs; you're only concerned on off-loading the work onto a background process and returning a web page as soon as possible.
And from examining the Rails documentation, it looks like deliver_signup_notification will block long enough to get the mail queued (although I may be wrong). So using a thread here might make your application seem more responsive, depending on how your mailer is configured.
Unfortunately, it's not clear to me that deliver_signup_notification is necessarily thread-safe. I'd want to read the documentation carefully before relying on that.
Note also that you're making assumptions about the lifetime of a Rails process once a request has been served. Many Rails applications using DRb (or a similar tool) to offload these background tasks onto an entirely separate worker process. The easiest way to do this changes fairly often--see Google for a number of popular libraries.
I have used your exact strategy and our applications are currently running in production (but rails 2.2.2). I've kept a close eye on it and our load has been relatively low (Less than 20 emails sent per day average, with peaks of around 150/day).
So far we have noticed no problems, and this appears to have resolved several performance issues we were having when using Google's mailserver.
If you need something in a hurry then give it a shot, it has been working for us.
They'll be the same as far as I know.