I'm planning to have a Rails App that has a very content rich interactive page where many users will connect to.
Development has went well and small time testing on the Dev servers went without a hitch either.
Problems started when we started alpha testing with selected groups of people. the sever would grind to a halt suddenly. Nginx would stop because of queue being full. I was at a lose for a while, but after looking around, came to the conclusion that the live actioncable was completely eating up my memory.This especially gets bad when the user reloads the page multiple times that subscribes to actioncable, causing additional process to become active, completely stopping the server, only being cured by a nginx reboot.
I currently run a 2core 1GB memory SSD run VPS server for alpha testing, perhaps at tops 20 concurrent users.Should I be running into performance problems with such load? or should tuning the code or redis, passenger fix this?
I know its hard to say any definitive things without more specifics, but could a ballpark estimate be done with the information?
After some gogoling and testing Nginx settings, adding this directive to the nginx settings for passenger has seemed to dramatically improve the performance issue.
location /special_websocket_endpoint {
passenger_app_group_name foo_websocket;
passenger_force_max_concurrent_requests_per_process 0;
}
more info here
https://www.phusionpassenger.com/library/config/nginx/tuning_sse_and_websockets/
20 concurrent users plus multiple tabs per user is still less than about 100 concurrent websocket connections, it is not that lot.
First thing I'd look for is leaks - when for some reason websocket connection or other resources (open files etc.) does not get freed when actual user disconnects. Make sure you're running fresh versions of rails/passenger, as there was a bug in rails causing similar behaviour (see https://blog.phusion.nl/2016/07/07/actioncable-under-stress-p1/ for details)
Also while actioncable+passenger inside nginx allows you to run everything inside single process, it is not a good idea when you expect some load.
When running a clean nginx and separate rails servers for regular requests and cable - at least other parts of the app will continue some kind of working in such conditions.
NewRelic is showing me that over 80% of execution time in the app server is taking place in "Middleware ActiveRecord::QueryCache#call"
Here is a gist of the relevant code tested (although I see similar results on other API endpoints).
Gist
I'm running the app server on AWS Elastic Beanstalk on a t2.medium instance and a t2.small Postgres RDS DB with max_connections set to 100. I'm testing this via loader.io, doing a test of 100 users with the maintain client load setting (this means about 6000 requests a minute).
Does anyone have an idea why the QueryCache is taking so much time?
Unfortunately, this issue with QueryCache is quite common and seems to have multiple causes, but the most common is that the connection between your EC2 app server and DB was temporarily severed, and QueryCache doesn't handle this particularly well.
Remedies include increasing your default connection pool size substantially (e.g. an order of magnitude higher), disabling QueryCache entirely, or increasing read_timeout in database.yml to 15 seconds or more depending on your environment.
If the read_timeout setting resolves the problem, you may want to investigate why there are so many disconnects between your app server and db.
Another path which might not be an option for you would be to run the app server on the same machine as the db, but that doesn't work for everyone due to their architecture. It certainly can be an effective test to see if eliminating the network variable helps. Good luck.
We are running 2 rails application on server with 4GB of ram. Both servers use rails 3.2.1 and when run in either development or production mode, the servers eat away ram at incredible speed consuming up-to 1.07GB ram each day. Keeping the server running for just 4 days triggered all memory alarms in monitoring and we had just 98MB ram free.
We tried active-record optimization related to bloating but still no effect. Please help us figure out how can we trace the issue that which of the controller is at fault.
Using mysql database and webrick server.
Thanks!
This is incredibly hard to answer, without looking into the project details itself. Though I am quite sure you won't be using Webrick in your target production build(right?), so check if it behaves the same under Passenger or whatever is your choice.
Also without knowing the details of the project I would suggest looking at features like generating pdfs, csv parsing, etc. Seen a case, where generating pdf files have been eating resources in a similar fashion, leaving like 5mb of not garbage collected memory for each run.
Good luck.
I have been working to deploy a relatively large Rails app (Rails 2.3.5) and recently doing some load testing we discovered that the throughput for the site is way below the expected level of traffic.
We were running on a standard 32bit server, 3GB of RAM with Centos, and we were running Ruby Enterprise Edition (latest build), Passenger (Latest build) and Nginx (Latest build) - when there is only one or two users the site runs fine (as you would expect) however when we try to ramp up the load to ~50 concurrent requests it completely dies. (Apache Bench report ~2.3 req/sec, which is terrible)
We are running RPM and trying to determine where the load issue is, but it's pretty evenly distributed across Rails, SQL and Memcached, so we're more or less going through and optimizing the codebase.
Out of sheer desperation we spun up a large EC2 instance (Ubuntu 9.10, 7.5GB RAM, 2 Compute Units/Cores) and setup the same configuration as the original server, and while there are more resources we were still seeing pathetic results.
So, after spending too much time trying to optimize, playing with caching configuration etc I decided to test the throughput of some mongrels, and ta-da, they are performing much much better then Passenger.
Currently the configuration is 15x Mongrels being proxied via Nginx, and we seem to be meeting our load requirements just but it's not quite enough to make me comfortable with going live... What I was wondering is if anyone knows of some possible causes for this...?
My configuration for passenger/nginx was:
Nginx workers: tried between 1 and 10, usually three though.
Passenger max pool size: 10 - 30 (yes, these numbers are quite high)
Passenger global queueing: tried both on and off.
NGinx GZip on: yes
It might pay to note that we had increased the nginx max client body size to 200m to allow for large file uploads.
Anyway suggestions would be really appreciated, while the mongrels are working fine it changes how we do things a lot and I would really prefer to use Passenger - besides, wasn't it supposed to make this easier and perform better?
Maybe your sql pool size is too small? This essentially limits the parallelism of database workloads in your application which in turn builds up to much increased load as soon as you put work on your app stack...
As a first step I would deploy a minimal "Hello World" type Rails application to your environment and see what throughput you get with that. Doing that will at least tell you if your problem is with the environment or somewhere in your application.
I have a simple Rails app deployed on a 500 MB Slicehost VPN. I'm the only one who uses the app. When I run it on my laptop, it's fast enough. But the deployed version is insanely slow. It take 6 to 10 seconds to load the login screen.
I would like to find out why it's so slow. Is it my code? (Don't think so because it's much faster locally, but maybe.) Is it Slicehost's server being overloaded? Is it the Internet?
Can someone suggest a technique or set of steps I can take to help narrow down the cause of this problem?
Update:
Sorry forgot to mention. I'm running it under CentOS 5 using Phusion Passenger (AKA mod_rails or mod_rack).
If it is just slow on the first time you load it is probably because of passenger killing the process due to inactivity. I don't remember all the details but I do recall reading people who used cron jobs to keep at least one process alive to avoid this lag that can occur with passenger needed to reload the environment.
Edit: more details here
Specifically - pool idle time defaults to 2 minutes which means after two minutes of idling passenger would have to reload the environment to serve the next request.
First, find out if there's a particularly slow response from the server. Use Firefox and the Firebug plugin to see how long each component (including JavaScript and graphics) takes to download. Assuming the main page itself is what is taking all the time, you can start profiling the application. You'll need to find a good profiler, and as I don't actually work in Ruby on Rails, I can't suggest any: google "profile ruby on rails" for some options.
As YenTheFirst points out, the server software and config you're using may contribute to a slowdown, but A) slicehost doesn't choose that, you do, as Slicehost just provides very raw server "slices" that you can treat as dedicated machines. B) you're unlikely to see a script that runs instantly suddenly take 6 seconds just because it's running as CGI. Something else must be going on. Check how much RAM you're using: have you gone into swap? Is the login slow only the first time it's hit indicating some startup issue, or is it always that slow? Is static content served slow? That'd tend to mean some network issue (either on the Slicehost side, or your local network) is slowing things down, assuming you're not in swap.
When you say "fast enough" you're being vague: does the laptop version take 1 second to the Slicehost 6? That wouldn't be entirely surprising, if the laptop is decent: after all, the reason slices are cheap is because they're a fraction of a full server. You're using probably 1/32 of an 8 core machine at Slicehost, as opposed to both cores of a modern laptop. The Slicehost cores are quick, but your laptop could be a screamer compared to 1/4 of core. :)
Try to pint point where the slowness lies
1/ application is slow, or infrastructure (network + web server)
put a static file on your web server, and access it through your browser
2/ If it is fast, it is probable a problem with application + server configuration.
database access is slow
try a page with a simpel loop: is it slow?
3/ If it slow, it is probably your infrastructure. You can check:
bad network connection: do a packet capture (with Wireshark for example) and look for retransmissions, duplicate packets, etc.
DNS resolution is slow?
server is misconfigured?
etc.
What is Slicehost using to serve it?
Fast options are things like: Mongrel, or apache's mod_rails (also called passenger phusion or
something like that)
These are dedicated servers (or plugins to servers) which run an instance of your rails app.
If your host isn't using that, then it's probably defaulting to CGI. Rails comes with a simple CGI script that will serve the page, but it reloads the app for every page.
(edit: I suspect that this is the most likely case, that your app is running off of the CGI in /webapp_directory/public/dispatch.cgi, which would explain the slowness. This tends to be a default deployment on many hosts, since it doesn't require extra configuration on their part, but it doesn't give good performance)
If your host supports "Fast CGI", rails supports that too. Fast CGI will open a CGI session, and keep it open for multiple pages, so you get much better performance, but it's not nearly as good as Mongrel or mod_rails.
Secondly, is it in 'production' or 'development' mode? The easy way to tell is to go to a page in your app that gives an error. If it shows you a stack trace, it's in development mode, which is slower than production mode. Mongrel and mod_rails have startup options to determine whether to run the app in production or development mode.
Finally, if your database is slow for whatever reason, that will be a big bottleneck as well. If you do have a good deployment (Mongrel/mod_rails/etc.) in production mode, try looking into that.
Do you have a lot of data in your DB? I would double check that you have indexed all the appropriate columns- because this can make a huge difference. On your local dev system, you probably have a lot more memory than on your 500 mb slice, which would result in the DB running a lot slower if you have big, un indexed tables. You can also run the slow queries logger in MySql to pinpoint columns without indexes.
Other than that, yes- passenger will need to spool up a process for you if you have not been using the site recently. If this is the case, you should see a significant speed increase on second, and especially third and later page loads.
You might want to run a local virtual machine with 500 MB. Are you doing a lot of client-server interaction? Delays over the WAN are significant
You might want to check out RPM (there's a free "lite" version too) and/or New Relic's Tune Up.
Your CPU time is guaranteed by Slicehost using the Xen virtualization system, so it's not that. Don't have the other answers for you, sorry! Might try 'top' on a console while you're trying to access the page.
If you are using FireFox and doing localhost testing (or maybe even on LAN) you may want to try editing the network.dns.disableIPv6 setting.
Type about:config in the address bar and filter for network.dns.disableIPv6 and double-click to set to true.
This bug has been reported mainly from Vista OS's, but some others as well.
You could try running 'top' when you SSH in to see which process is heavy. If you also have problems logging you, perhaps you may try getting Statistics in the Slicehost manager.
If you discover it is MySQL's fault, consider decreasing the number of servers it can spawn.
512 seems decent for Rails application, you might have to check if you misconfigured too.