Let me start off by saying I understand performance is hard, and even harder through a forum, but I hope someone can point me towards the next step of figuring out this problem we're having in production on a Ruby on Rails environment. I've been seeing this for a while, but now with our usage down due to Covid, it's become more clear that it's not a user-load issue, but something in the infrastructure.
The day starts off fine, but midday, things slow more and more... until a passenger restart clears everything up for 24/48/96 hours.
Checking the obvious items:
Server memory usage is in check. Memory use increases during this time from 20%-30%. So some increase, but definitely not swapping (I've seen that happen before)
CPU usage is similar. It increases from 1% at 6am to 18% at worst case, but still well within the capabilities of the server.
Passenger usage. Looking at passenger-status, there's never a backlog of requests. Because of covid, our user-base is down, and even at its slowest, I'm seeing 2-3 passenger processes serving content (out of ~40 max), and no long-running requests.
Delayed job workers (3) are running, but no jobs at the time. They don't seem to be using a significant amount of cpu or mem
Watching the apache/rails logs, nothing looks awry. No DoSes, no unexpected load.
Looking at long-running transactions in NewRelic, there are some that are taking 20-30-50 sec, but after the passenger restart, they are back to 1-3 sec like usual. All the time is in Ruby.
So this is where I'm stuck. I can see where the problem is (185 sec):
but if I restart passenger and re-run, that same code will take less than a second. And that's just the example that I see from today's traces. Yesterday, it looked like it was a different controller having problems.
Any recommendations on my next steps to troubleshoot? I don't know if I should instrument a specific controller, because it's not just one method that's causing the problem (afaik). I think I'm seeing the symptoms, not the cause - and no idea how to see what's really going on.
Thanks in advance
-Mike
Rails 4.2.11.1
Ruby 2.4.9
Passenger 6.0.5 on Apache 2.4.43
Related
I have an app running on Heroku with a few thousand visitors per day. I do not update it very often as it runs well anyway. Recently, however, I started getting memory increases in a way I have never had before. I am 98% sure it does not have to do with any changes in the code that I have done, as I have not done anything to the code in quite a while. I know from experience that tracing down memory issues is extremely difficult and time-consuming - and at the moment I don't have the time to do it.
Considering the fact that I get this stair-case increase in memory over time (over the course of a few hours) once a day, is there a quick and dirty way of just restarting the server once it starts doing so, so it won't slow down the server for those hours? Like
RestartApp if ServerMemory > 500 Mb
or the likes of it?
I am running ruby 2.4.7 (is that likely an issue in terms of memory increases?) and Rails 4.2.10
Lately we've had trouble on our Rais 4.2.7.1 app every night, we start seeing a bunch of really slow ActiveRecord::QueryCache#call calls even though our traffic is relatively low in the middle of the night:
We're running on Heroku using Puma and the app is very job heavy, for which we use Sidekiq. During the day it works fine but every night we get these spikes of extremely slow response times via the API that seem to originate with ActiveRecord::QueryCache#call.
The only thing I can find from our app that might be causing this is we have heroku pg:backups enabled, and the night of the above image the backup began running at 3:06 which is the exact time you see that first ActiveRecord::QueryCache#call spike in the newrelic graph. The backup finished an hour later, however (around the biggest spike), but as you can see the spikes continued until around 5am.
Could this be caused by pg:backups? (Our database is about 19GB), or could it be something else entirely? Is there a good way to avoid this cache call or speed it up? I don't fully understand WHY it would be so slow or exist at all in the transaction list. Any recommendations?
Funnily enough, we've been investigating this lately after seeing similar behaviour. There is a definite performance hit caused by pg:backups on large databases. Notice the big spike just after 1am, when backup kicks in:
DB size is >100GB
It's not that surprising, and in fact Heroku do have documentation on this, which suggests that you should only use pg:backups for databases under 20GB.
For larger databases, creating a follower and taking the backup from that is preferable. Annoyingly for high availability databases, it doesn't appear that you can read from the standby.
I can't shed much light on ActiveRecord::QueryCache though, so the rest of this post is speculation, and maybe the starting point for further investigation. Happy to delete/amend if someone more knowledgable can weigh in :-)
Heroku's docs do say that the backup process will evict well cached data from non-Postgres caches, so this could represent your workers repopulating that cache many times over.
It may also be worth having a look at this. Could your workers be reusing connections and receiving dirty query caches?
We are running a big server (12 threads, 6 cores, 64Gb ram, 2 SDDs raid-0) for our rails app deployed with nginx/passenger.
Unfortunately, pages are taken forever to load something like between 10 and 40 seconds. However, the server is under a really light load, with a load average of 0.61 0.56 0.53. We have ram used weirdly, free -ml reporting 57Gb (of 64Gb) usage whereas htop reporting only 4Gb (of 64Gb).
We have checked our production log, and rails request takes something like 100/200ms to be completed, so almost nothing.
How can we identify the bottleneck?
This question is fairly vague, but I'll see if I can give you some pointers.
My first guess is that your app is spending a lot of time doing database related stuff, see below for my advice.
As for the odd memory usage, are you looking at the correct part of the free -ml output? Just to clarify, you want to be looking at the -/+ buffers/cache: line to get the accurate output.
You might also check to see if any of your passenger workers are hanging, as that is a fairly common issue with passenger. You can do this by running strace -p $pid on your passenger workers. If its hanging, it will have an obvious lack of "doing anything"
As for troubleshooting response time within rails itself, I would highly suggest looking into using newrelic(http://newrelic.com/). You can often times see exactly which part of your app is causing the bad response time that way by breaking down how much time is spent in each part of your app. It's a simple gem to install and once you get reporting working, its pretty invaluable for issues like this.
Finally, the bottleneck was passenger, passenger-status is pretty useful showing up the queue left.
Our server is pretty precent so we just increase the number of passenger processes in nginx.conf to 600, resulting:
passenger_root /usr/local/rvm/gems/ruby-2.0.0-p195/gems/passenger-4.0.5;
passenger_ruby /usr/local/rvm/wrappers/ruby-2.0.0-p195/ruby;
passenger_max_pool_size 600;
I'm running a Rails app through Phusion Passenger (mod_rails) which will run smoothly for a while, then suddenly slow to a crawl (one or two requests per hour) and become unresponsive. CPU usage is low throughout the whole ordeal, although I'm not sure about memory.
Does anyone know where I should start to diagnose/fix the problem?
Update: restarting the app every now and then does fix the problem, although I'm looking for a more long-term solution. Memory usage gradually increases (initially ~30mb per instance, becomes 40mb after an hour, gets to 60 or 70mb by the time it crashes).
New Relic can show you combined memory usage. Engine Yard recommends tools like Rack::Bug, MemoryLogic or Oink. Here's a nice article on something similar that you might find useful.
If restarting the app cures the problem, looking at its resource usage would be a good place to start.
Sounds like you have a memory leak of some sort. If you'd like to bandaid the issue you can try setting the PassengerMaxRequests to something a bit lower until you figure out what's going on.
http://www.modrails.com/documentation/Users%20guide%20Apache.html#PassengerMaxRequests
This will restart your instances, individually, after they've served a set number of requests. You may have to fiddle with it to find the sweet spot where they are restarting automatically before they lock up.
Other tips are:
-Go through your plugins/gems and make sure they are up to date
-Check for heavy actions and requests where there is a lot of memory consumption (NewRelic is great for this)
-You may want to consider switching to REE as it has better garbage collection
Finally, you may want to set a cron job that looks at your currently running passenger instances and kills them if they are over a certain memory threshold. Passenger will handle restarting them.
i'm running a rails application with apache+passenger on virtual servers that do not have any swap space configured.
The site gets decent amount of traffic with 200K+ daily requests and sometimes the whole system runs out of memory causing odd behaviour on whole system.
The question is that is there any way to configure apache or passenger not to run out of memory (e.g. gracefully restarting passenger instances when they start using, say more than 300M of memory).
Servers have 4GB of memory and currently i'm using passenger's PassengerMaxRequests option but it does not seem to be the most solid solution here.
At the moment, i also cannot switch to nginx so that is not an option to preserve some room.
Any clever ideas i'm probably missing are welcome.
Edit: My temporary solution
I did not go with restarting Rails instances when they exceed certain amount of memory usage. Engine Yard wrote great blog post on the ActiveRecord memory bloat issue. This is our main suspect on the subject. As i did not have much time to optimize application, i set PassengerMaxRequests to 300 and added extra 2GB memory to server. Things have been good since then. At first i was worried that re-starting Rails instances continuously makes it slow but it does not seem to have impact i should worry about.
If you mean "limiting" as killing those processes and if this is the only application on the server and it is a Linux, then you have two choices:
Set maximum amount of memory one process can have:
# ulimit -m
unlimited
Or use cgroups for similar behavior:
http://en.wikipedia.org/wiki/Cgroups
I would advise against restarting instances (if that is possible) that go over the "memory limit", because that may put your system in infinite loops where a process repeatedly reaches that limit and restarts.
Maybe you could write a simple daemon that constantly watches the processes, and kills any that go over a certain amount of memory. Be sure to log any information about the process that did this so you can fix the issue whenever it comes up.
I'd also look into getting some real swap space on there... This seems like a bad hack.
I have a problem where passenger processes end up going out of control and consuming too much memory. I wrote the following script which has been helping to keep things under control until I find the real solution http://www.codeotaku.com/blog/2012-06/passenger-memory-check/index. It might be helpful.
Passenger web instances don't contain important state (generally speaking) so killing them isn't normally a process, and passenger will restart them as and when required.
I don't have a canned solution but you might want to use two commands that ship with Passenger to keep track of memory usage and nr of processes: passenger-status and sudo passenger-memory-stats, see
Passenger users guide for Nginx or
Passenger users guide for Apache.