In my user model I have a friends method that returns the hash of all the user's facebook friends. In my view I iterate through the entire list to paginate that list alphabetically. I can't tell if my server is running really slow or if this is extremely inefficient. How can I make this process faster? Is it better to maybe create a friendsmodel? Please let me know if my method is inefficient, why, and how I might be able to make it faster. Thanks!
In my Home.html.erb view I have <%letter ='a'%> which changes when the user selects a different letter and the page refreshes.
<% current_user.friends.each do |user| %>
<% if user['name'].downcase.start_with? letter %>
do something
<% end %>
User Model
def facebook
#facebook ||= Koala::Facebook::API.new(token)
block_given? ? yield(#facebook) : #facebook
rescue Koala::Facebook::APIError => e
logger.info e.to_s
nil
end
def friends
facebook {|fb| fb.get_connections("me","friends")}.sort{|a,b| a['name']<=>b['name']}
end
You are making an external API call for every request. Plus user may have good number of friends like 500, 1000.
I in my fb app processing the data in background job(delayed job). You can use resque or sidekiq or some other background to process user data.
I would suggest you to make Friend model and have its association with users model. Then if you have some n+1 query problem you can use includes and instead of using sort use order it would be much faster then sort. Moreover instead of using each use find_each it will process the data in chunks you can google the difference between each and find_each. hope it would be helpful
One thing that will be slowing down each request for sure is the fact that your making an external API call in the middle of the request. The second thing to note is that your potentially bringing back a large amount of data, easily getting into the hundreds, if not thousands.
A more appropriate way to handle this would be to create a Friend model where each friend has a belongs to relationship to the User. In a background processor (ie delayed job, resque, sidekiq), iterate through your users and update their friends at some interval that your server can tolerate. It will cause some lag as to when the user's friends will show up. You'll have to be the judge as to how much lag time is tolerable, and it depends largely on your number of users and budget for hardware.
This is effectively a caching mechanism, and you may want to account for the fact that data will change, friends may be removed and so on. You could delete all the friends and recreate the whole list on each refresh. Doing so inside a transaction will keep the deletes from showing up until it is commited.
Related
I have a RoR application which contains an API to manage applications, each of which contain recipes (and groups, ingredients, measurements).
Once the user has finished managing the recipes, they download a JSON file of the entire application. Because each application could have hundreds of recipes, the files can be large. It also means there is a lot of DB calls to get all the required data to export.
Now because of this, the request to download the application can take upwards of 30 seconds, sometimes more.
My current code looks something like this:
application.categories.each do |c|
c.recipes.each do |r|
r.groups.each do |r|
r.ingredients.each do |r|
Within each loop I'm storing the data in a HASH and then giving it to the user.
My question is: where do I go from here?
Is there a way to grab all the data I require from the DB in one query? From looking at the log, I can see it is running hundreds of queries.
If the above solution is still slow, is this something I should put into a background process, and then email the user a link (or similar)?
There are of course ways to grab more data at once. This is done with Rails includes or joins, depending on your needs. See this article for some detailed information.
The basic idea is that you can join between your tables so that each time new queries aren't generated. When you do application.categories, that's one query. For each of those categories, you'll do another query: c.recipes - this creates N+1 queries, where N is the number of categories you have. Rather, you can include them off the get go to create 1 or 2 queries (depending on what Rails does).
The basic syntax is easy:
Application.includes(:categories => :recipes).each do |application| ...
This generates 1 (or 2 - again, see article) query that grabs all applications, their categories, and each categories recipies all at once. You can tack on the groups and ingredients too.
As for putting the work in the background, my suggestion would be to just have a loading image, or get fancy by using a progress bar.
First of all I have to assume that the required has_many and belongs_to associations exist.
Generally you can do something like
c.recipes.includes(:groups)
or even
c.recipes.includes(:groups => :ingredients)
which will fetch recipes and groups (and ingredients) at once.
But since you have a quite big data set IMO it would be better if you limited that technique to the deepest levels.
The most usefull approach would be to use find_each and includes together.
(find_each fetches the items in batches in order to keep the memory usage low)
perhaps something like
application.categories.each do |c|
c.recipes.find_each do |r|
r.groups.includes(:ingredients).each do |r|
r.ingredients.each do |r|
...
end
end
end
end
Now even that can take quite a long time (for an http request) so you can consider using some async processing where the client will generate a request that is going to be processed by the server as a background job, and when that is ready, you can provide a download link (or send an email) to the client.
Resque is one possible solution for handling the async part.
I have a website where I need to be able to display on each user's profile the last time they were "active" on the site. In this case, "active" is defined by browsing content, interacting with other users and completing courses.
My plan is to have a last_active column on the Users table, which I can update with Time.now. The question is, how do I do this without hitting up the database during every single controller action? That seems... expensive. For example, I want to avoid doing this:
# In each controller
def index
current_user.activity
end
# In the User model
def activity
self.update_attribute(:last_active, Time.now)
end
Because then every time a user gets the content listing, I have to make a database call.
The other option would be to have an Activity table, which I update with various user actions (kind of like audits). That would allow me to store and display more relevant information about what users are doing. But that goes back to the same question: how do I update these tables without massive overhead?
It's really a rather moot question – No, there is no way to update the database without updating the database.
If you wanted to get complicated, you could try to do some client-side scripting to store that information in a session variable or a cookie, and only commit it to the db once in a while, but that seems like a lot of work for a small feature.
Maybe if you add an index to your :last_active column you make it marginally less expensive? But otherwise, I would just go for it, and try to be conservative about how often it's updated.
You could also check if Time.now > #user.last_active+10.minutes before updating to make sure that you aren't constantly writing to the db, but then your just querying instead which may not be better...
I don't think there is a way around the overhead without restricting when you update a particular user's 'last active' attribute.
So as Charlie Egan alluded to, you have two options:
Only update the 'last active' attribute when the user logs in. You'll still get a decent sense of a user's general activity on the site just by doing this.
Or
Only update the 'last active' attribute on certain activity. For example, you mentioned in your question that users can complete courses. That seems like a fairly significant 'activity', so update the 'last active' attribute. Less significant activities, like browsing content can be ignored.
Don't you think about redis|memcache|any_in_memory_storage for such data?
If you're fine with async updates, you could set up a delayed resque job, deleting previous jobs.
Resque.remove_delayed_selection RecordLastUserActivity, {
|args| args[0]['user_id'] == current_user.id
}
Resque.enqueue_at(10.minutes.from_now, RecordLastUserActivity,
user_id: current_user.id, last_seen_at: Time.now)
Not sure if this will provide greater perfomance though, it will require some testing.
I'm hoping to get advice on the proper use of caching to speed up a timeline query in Rails. Here's the background:
I'm developing an iPhone app with a Rails backend. It's a social app, and like other social apps, its primary view is a timeline (i.e., newsfeed) of messages. This works very much like Twitter, where the timeline is made up of messages of the user and of his/her followers. The main query in the API request to retrieve the timeline is the following:
#messages = Message.where("user_id in (?) OR user_id = ?", current_user.followed_users.map(&:id), current_user)
Now this query gets quite inefficient, particularly at scale, so I'm looking into caching. Here are the two things I'm planning to do:
1) Use Redis to cache timelines as lists of message ids
Part of what makes this query so expensive is figuring out which messages to display on-the-fly. My plan here is to keep create a Redis list of message ids for each user. Assuming I build this correctly when a Timeline API request comes in I can call Redis to get a pre-processed ordered list of the ids of the messages to display. For example, I might get something like this: "[21, 18, 15, 14, 8, 5]"
2) Use Memcached to cache individual message objects
While I believe the first point will help a great deal, there's still the potential problem of retrieving the individual message objects from the database. The message objects can get quite big. With them, I return related objects like comments, likes, the user, etc. Ideally, I would cache these individual message objects as well. This is where I'm confused.
Without caching, I would simply make a query call like this to retrieve the message objects:
#messages = Message.where("id in (?)", ids_from_redis)
Then I would return the timeline:
respond_with(:messages => #messages.as_json) # includes related likes, comments, user, etc.
Now given my desire to utilize Memcache to retrieve individual message objects, it seems like I need to retrieve the messages one at a time. Using psuedo-code I'm thinking something like this:
ids_from_redis.each do |m|
message = Rails.cache.fetch("message_#{m}") do
Message.find(m).as_json
end
#messages << message
end
Here are my two specific questions (sorry for the lengthy build):
1) Does this approach generally make sense (redis for lists, memcached for objects)?
2) Specifically, on the pseudo-code below, is this the only way to do this? It feels inefficient grabbing the messages one-by-one but I'm not sure how else to do it given my intention to do object-level caching.
Appreciate any feedback as this is my first time attempting something like this.
On the face of it, this seems reasonable. Redis is well suited to storing lists etc, can be made persistent etc, and memcached will be very fast for retrieving individual messages, even if you call it sequentially like that.
The issue here is that you're going to need to clear/supplement that redis cache each time a message is posted. It seems a bit of a waste just to clear the cache in this circumstance, because you'll already have gone to the trouble of identifying every recipient of the message.
So, without wishing to answer the wrong question, have you thought about 'rendering' the visibility of messages into the database (or redis, for that matter) when each message is posted? Something like this:
class Message
belongs_to :sender
has_many :visibilities
before_create :render_visibility
sender.followers.each do |follower|
visibilities.build(:user => follower)
end
def
end
You could then render the list of messages quite simply:
class User
has_many :visibilities
has_many :messages, :through => :visibilities
end
# in your timeline view:
<%= current_user.messages.each { |message| render message } %>
I would then add of individual messages like this:
# In your message partial, caching individual rendered messages:
<%= cache(message) do %>
<!-- render your message here -->
<% end %>
I would also then add caching of entire timelines like this:
# In your timeline view
<%= cache("timeline-for-#{current_user}-#{current_user.messages.last.cache_key}") do %>
<%= current_user.messages.each { |message| render message } %>
<% end %>
What this should achieve (I've not tested it) is that the entire timeline HTML will be cached until a new message is posted. When that happens, the timeline will be re-rendered, but all the individual messages will come from the cache rather than being rendered again (with the possible exception of any new ones that haven't been viewed by anyone else!)
Note that this assumes that the message rendering is the same for every user. If it isn't, you'll need to cache the messages per user too, which would be a bit of a shame, so try not to do this if you can!
FWIW, I believe this is vaguely (and I mean vaguely) what twitter do. They have a 'big data' approach to it though, where the tweets are exploded and inserted into follower timelines across a large cluster of machines. What I've described here will struggle to scale in a write-heavy environment with lots of followers, although you could improve this somewhat by using resque or similar.
P.S. I've been a bit lazy with the code here - you should look to refactor this to move e.g. the timeline cache key generation into a helper and/or the person model.
I have an RoR application like posting answers to a question. If a user answers to a question, notification messages are sent to all the users, who watch-listed the question, who tracks the question and to the owner of the question. I am using delayed jobs for creating the notification messages. so, While creating answer, there are many inserts into delayed job table going on,which is slowing down the page load. It takes more time to redirect to the question show page after the answer is created.
Currently I am inserting into answers table using AJAX request. Is there any way to insert into delayed jobs table in background after the AJAX request completes?
As we have been trying to say in comments:
It sounds like you have something like:
User.all.each do |user|
user.delay.some_long_operation
end
This ends up inserting a lot of rows into delayed_jobs. What we are suggesting is to refactor that code into the delayed job itself, roughly:
def delayed_operation
User.all.each do |user|
user.some_long_operation
end
end
self.delay.delayed_operation
Obviously, you'll have to adapt that, and probably put the delayed_operation into a model library somewhere, maybe as a class method... but the point is to put the delay call outside the big query and loop.
I really advice doing this like that in a separate process. Why has the user to wait for those meta-actions? Stick to delivering a result page and only notifying your server something has to be done.
Create a separate model PostponedAction to build a list of 'to-do' actions. If you post an answer, add one PostponedAction to this database, with a parameter of the answer id. Then give the results back to the user.
Use a separate process (cron job), to read the PostponedAction items, and handle those. Mark them as 'handled' or delete on succesfull handling. This way, the user is not bugged by slow server processes.
Beside the email jobs you currently have, invent another type of job handling the creation of these jobs.
def email_all
User.all.each do |user|
user.delay.email_one()
end
end
def email_one
# do the emailing
end
self.delay.email_all()
This way the user action only triggers one insert before they see the response. You can also track individual jobs.
So I've got a forum thread full of posts, and I want to eager load the users from the posts and those users roles, to reduce the total number of database queries (which seems to be the best way to do things)
(to make things extra fun, forum and posts are nested resources, if that makes a differnece)
def show
#forum = Forum.find(params[:forum_id])
#posts = #forum.posts.includes(:user => :role).where('id = ? OR parent_post_id =?',params[:id], params[:id])
end
The page renders, but I can't really tell by looking at the console if it's actually reducing the number of queries or not. The console appears to have a slight reduction in number of queries to the CACHE, but the Load calls holds steady. Am I doing this right?
yes, I think so, if the eager loading is successful, the query count will be reduced.
If you are using MYsql, I suggest you use "query_reviewer". ( https://github.com/dsboulder/query_reviewer) it will show your how many queries were executed for opening a page.