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Ruby on Rails load testing habits

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Re: Ruby on Rails load testing habits

#31

Post by jmuguy »

ndriscoll wrote: post #29
_chap wrote: post #26

Earlier quoted context omitted.

Rails supports multiple threads: https://guides.rubyonrails.org/threading_and_code_execution.... Rails has some tooling to help with query bloat: https://guides.rubyonrails.org/active_record_querying.html#e...

Interesting. My understanding is that part of why mastodon is so slow/resource hungry is that it serializes background tasks to redis for a sidecar process to pick up, and that that's the normal way to do things. If rails has a concurrent runtime, why don't they just run background work directly?

Rails isn't super opinionated about database writes, its mostly left up to developers to discover that for relational DBs you do not want to be doing a bunch of small writes all at once.

That said it specifically has tools to address this that started appearing a few years ago https://github.com/rails/rails/pull/35077

The way my team handles it is to stick Kafka in between whats generating the records (for us, a bunch of web scraping workers) and and a consumer that pulls off the Kafka queue and runs an insert when its internal buffer reaches around 50k rows.

Rails is also looking to add some more direct background type work with https://github.com/basecamp/solid_queue but this is still very new - most larger Rails shops are going to be running a second system and a gem called Sidekiq that pulls jobs out of Redis.

In terms of read queries, again I think that comes down to the individual team realizing (hopefully very early in their careers) that's something that needs to be considered. Rails isn't going to stop you from doing N+1 type mistakes or hammering your DB with 30 separate queries for each page load. But it has plenty of tools and documentation on how to do that better.

Re: Ruby on Rails load testing habits

#32

Post by ndriscoll »

jmuguy wrote: post #31
ndriscoll wrote: post #29

Earlier quoted context omitted.

Interesting. My understanding is that part of why mastodon is so slow/resource hungry is that it serializes background tasks to redis for a sidecar process to pick up, and that that's the normal way to do things. If rails has a concurrent runtime, why don't they just run background work directly?

Rails isn't super opinionated about database writes, its mostly left up to developers to discover that for relational DBs you do not want to be doing a bunch of small writes all at once. That said it specifically has tools to address this that started appearing a few years ago https://github.com/rails/rails/pull/35077 The way my team handles it is to stick Kafka in between whats generating the records (for us, a bunc…

`insert_all` seems to be an example of what I mean about how the framework encourages you to do the wrong thing. Here there is a lower-level hatch to do a bulk insert, but it says it doesn't run your callbacks/validations. So if you're using "good" design (or using libraries that work by hooking into that functionality), you can't use it. Laravel was the same way.

The new queue you linked is database backed, but the whole point is that you want to just run a job without needing to serialize anything outside of your process. It should just schedule it onto the thread pool and give you a promise for when it's done.

The Kafka thing also seems to be an example of what I mean: in Scala I'd just make a `new Queue` with a thread safe library, and have a worker pull off and do an insert every hundred rows or so, or after e.g. 5 ms have passed, whichever is first. No extra infrastructure needed, minimal RAM used, your queueing delay is in the single digit ms, and you get the scaling benefits. Takes maybe 10-20 lines of code.

You can then take that and abstract it into a repository pattern so that you could have an ORM that does batching for you with single item interfaces (for non-transactional workflows), but none of them seem to do this.

Re: Ruby on Rails load testing habits

#33

Post by jmuguy »

ndriscoll wrote: post #32
jmuguy wrote: post #31

Earlier quoted context omitted.

Rails isn't super opinionated about database writes, its mostly left up to developers to discover that for relational DBs you do not want to be doing a bunch of small writes all at once. That said it specifically has tools to address this that started appearing a few years ago https://github.com/rails/rails/pull/35077 The way my team handles it is to stick Kafka in between whats generating the records (for us, a bunc…

`insert_all` seems to be an example of what I mean about how the framework encourages you to do the wrong thing. Here there is a lower-level hatch to do a bulk insert, but it says it doesn't run your callbacks/validations. So if you're using "good" design (or using libraries that work by hooking into that functionality), you can't use it. Laravel was the same way. The new queue you linked is database backed, but the…

I supposed I've just been in Rails land for a while so I can't make an apples to apples comparison to how other frameworks approach things but I don't think insert_all is encouraging anything wrong - by the time a Rails team is reaching for it I can almost guarantee they understand the implications of it.

And again maybe I'm just not understanding but I really like having our background processes handled completely separately from our main web application. Maybe its just the peace of mind knowing that I can scale them independently of each other.

Re: Ruby on Rails load testing habits

#34

Post by ndriscoll »

jmuguy wrote: post #33
ndriscoll wrote: post #32

Earlier quoted context omitted.

`insert_all` seems to be an example of what I mean about how the framework encourages you to do the wrong thing. Here there is a lower-level hatch to do a bulk insert, but it says it doesn't run your callbacks/validations. So if you're using "good" design (or using libraries that work by hooking into that functionality), you can't use it. Laravel was the same way. The new queue you linked is database backed, but the…

I supposed I've just been in Rails land for a while so I can't make an apples to apples comparison to how other frameworks approach things but I don't think insert_all is encouraging anything wrong - by the time a Rails team is reaching for it I can almost guarantee they understand the implications of it. And again maybe I'm just not understanding but I really like having our background processes handled completely s…

It's not that insert_all is encouraging anything wrong; it's that the normal way to use ActiveRecord does. insert_all is the right way to do things performance-wise, so you'd want to use it when possible, but if you were using other features of the framework like callbacks/validations for create/update, then you can't. The happy-path of an ORM tends to push you in a direction where bad performance all over the place is the default, and it does it in a way where if you didn't have properly calibrated performance expectations, you might think that the bottleneck is because IO is slow, but actually it could easily handle 10x the workload with better access patterns.

Re: Ruby on Rails load testing habits

#35

Post by Rapzid »

eek2121 wrote: post #22
Hendrikto wrote: post #10

> If the application can’t saturate the CPU, there’s a fundamental problem. It’s a shame because it makes adding more servers less efficient. Money is being wasted on hosting costs, and this should be a priority to address. Talking about efficiency being a priority, but using RoR. I guess that is one way of saturating the CPU.

I have never seen Ruby on Rails be a bottleneck, and I have been using it since version 2. Most bottlenecks are either that database choices or poor code/design choices by developers. That is especially true today.

I'm biased as I usually come on to the scene because a company has a successful product and is experiencing engineering scaling pains.

That said, in my experience, CPU is often the ultimate bottleneck with PHP, Ruby, Python, and.. Like everything. Over the years serializers have often been a pain point; XML in PHP and RoR, and the Rails "serializers" currently. Any sort of mapping or hydration(which is a LOT of what happens in web apps) is comparatively slow, often order of magnitude or more, over something like nodejs, C#, golang, and etc.

> Most bottlenecks are either that database choices or poor code/design choices by developers

Perhaps in sheer quantity, but with experience those are often low hanging fruit. After those are addressed you are left with the pain of the language and framework inefficiencies.

Re: Ruby on Rails load testing habits

#36

Post by edgyquant »

ndriscoll wrote: post #29
_chap wrote: post #26

Earlier quoted context omitted.

Rails supports multiple threads: https://guides.rubyonrails.org/threading_and_code_execution.... Rails has some tooling to help with query bloat: https://guides.rubyonrails.org/active_record_querying.html#e...

Interesting. My understanding is that part of why mastodon is so slow/resource hungry is that it serializes background tasks to redis for a sidecar process to pick up, and that that's the normal way to do things. If rails has a concurrent runtime, why don't they just run background work directly?

Having a redis job queue is extremely standard, especially for web app development, regardless of language. For one thing if the web server crashes for any reason the jobs still continue processing and also you have a log of jobs in case they fail etc

Re: Ruby on Rails load testing habits

#37

Post by ndriscoll »

edgyquant wrote: post #36
ndriscoll wrote: post #29

Earlier quoted context omitted.

Interesting. My understanding is that part of why mastodon is so slow/resource hungry is that it serializes background tasks to redis for a sidecar process to pick up, and that that's the normal way to do things. If rails has a concurrent runtime, why don't they just run background work directly?

Having a redis job queue is extremely standard, especially for web app development, regardless of language. For one thing if the web server crashes for any reason the jobs still continue processing and also you have a log of jobs in case they fail etc

Are people using it for reliability though? Are they running redis in a mode where it persists a journal? If not, then if redis crashes for any reason, you're in the same situation.

And, like, Mastodon apparently uses a queue to do things like send new user registration emails. Why not just send the email from the new user request handler? Then if there's an error, you can tell the user in the response instead of saying "okay you should get an email" and then having it go into the ether. I was under the impression this had something to do with not wanting to tie up the HTTP worker because you want it to quickly get back to doing HTTP requests, but if it can concurrently process requests, there's no issue.

Similarly they have an ingest queue for other federated servers sending them updates. But if things are fast, why wouldn't they just process the updates in the HTTP handler? You don't need a reliable queue because if e.g. you crash, the other side will not get their HTTP response, and they'll know to retry.

Re: Ruby on Rails load testing habits

#38

Post by wdfx »

rdoherty wrote: post #8

These are great tips for load testing any web service. Don't forget that you can also saturate memory, disk or network too, so watch those graphs too. I've seen load tests unable to saturate CPU because another resource was limited. Also don't forget that you are load testing all the dependencies of your service. Database, caching tier, external services, etc. Make sure other teams are aware! Also nothing beats real…

> external services, etc. Make sure other teams are aware!

Guilty. I've had one of our partners call me one time because I'd caused a huge load on their end. Lots of apologies and embarrassment followed.

Later I mocked out those external calls with stubs which behaved similarly, in that I could specify the min/max/average wait times and error rates.

Re: Ruby on Rails load testing habits

#39

Post by hassy »

anonacct37 wrote: post #28
nomilk wrote: post #4

Earlier quoted context omitted.

I've never done load testing before, but would it be hard to write a script in pure ruby (maybe with a few libraries) that makes a lot of concurrent requests to whatever endpoints and using whatever params you like?

There's a lot of subtleties. It's really easy to accidentally load test the wrong part of your web application due to differences in compression, cache hit ratios, http settings, etc. Shameless self promotion but I wrote up a bunch of these issues in a post describing all the mistakes I have made so you can learn from them: https://shane.ai/posts/load-testing-tips/

This is a great blog post! just taking the opportunity here to comment on this:

> Finally for full scale high fidelity load tests there are relatively few tools out there for browser based load testing.

It exists as of a few months ago and it's fully open source: https://github.com/artilleryio/artillery (I'm the lead dev). You write a Playwright script, then run it in your own AWS account on serverless Fargate and scale it out horizontally as you see fit. Artillery takes care of spinning up and down all of the infra. It will also automatically grab and report Core Web Vitals for you from all those browser sessions, and we just released support for tracing so you can dig into the details of each session if you want to (OpenTelemetry based so works with most vendors- Datadago APM, New Relic etc)

Re: Ruby on Rails load testing habits

#40

Post by pistoriusp »

e12e wrote: post #21
pistoriusp wrote: post #14

Having your test database mirror production as closely as possible is also an important habit, however I’m biased since that’s part of the offering that I’m building.

You might want to try and maintain a synthetic dataset for testing and staging that has the same "shape" as your production data - to avoid exposing sensitive data. We're currently trying to have each rails model implement a #new_example method that builds a valid subgraph filled in by Faker, ready to save. Ie a user = User.new_example will come with a Company.new_example if every user needs a company relationship. S…

We're doing the same, but for the TypeScript world with "Snaplet Seed." We use generative AI to generate deterministic values + the required relational data: https://www.snaplet.dev/seed

We generate data based off of your database schema and your production data (if you give us access.)

Since you've kinda already built something like this I would be curious to hear what you think!

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