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If Youtrack uses Xodus as the underlying database then how can YouTrack handle scalability?

  1. Xodus write lock system prevents scalability of application built with the database (see: Remove lock on environment at every transaction end and https://youtrack.jetbrains.com/issue/XD-807)

In a typical Java server environment, when the server encounters more load, it spawns new processes of the same application (typically); this is where Xodus breaks since it's lock mechanism is always bound to the first process that used or accessed the environment.

So how does YouTrack, in general, get around this limitation and be able to work as a production web application?

quarks
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1 Answers1

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When it comes to scalability, the are two main design approaches to consider. Vertical scalability assumes that a single-node application can scale up with more CPU and more RAM added. Horizontal scalability, on the contrary, relies on multiple copies of the same application to handle the load. There's a great answer that goes into more details on both approaches. Although it uses database servers as an example, it is equally applicable to the most application types one can encounter today.

Horizontally scalable applications may seem more typical these days, as they are generally easier to implement. Any kind of a critical issue with your code, like a race condition, is likely to bring down a single node only. So this approach is a bit more forgiving to the programming errors we all make at times.

Xodus write lock system prevents scalability of application built with the database

Now it should be clear, that Xodus architecture disallows horizontally scalable solutions only. Vertically scalable applications in turn are perfectly fine with it. This also answers your question about YouTrack. It scales in a vertical manner and is quite good at it.

Jk1
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  • So you mean what YouTrack does is just scale the CPU and RAM? Are you by any chance working with the YouTrack team? And even so, this vertical scaling is also problematic with Xodus, see: https://github.com/nginx/unit/issues/396 – quarks Sep 08 '20 at 01:18
  • This is exactly what I mean. And I'm with JetBrains, yes. As of github.com/nginx/unit/issues/396, it does seem to be caused by Unit's single thread limitation. So what is really killing scalability in your particular case is a mix of Xodus and Unit. These two assume mutually exclusive approaches to scalability. – Jk1 Sep 08 '20 at 06:29
  • So, how do YouTrack scales in production using Xodus; if it can only run as one process and application cannot scale into multiple instances over more load? – quarks Sep 10 '20 at 15:42
  • YouTrack doesn't use things like Unit, so it is free to spawn as many threads as needed to handle the load. – Jk1 Sep 11 '20 at 09:38
  • You're right, but I wonder if there's a work-around: https://stackoverflow.com/questions/63887544/strategies-for-scaling-applications-vertically-or-horizontally – quarks Sep 14 '20 at 15:43
  • Hi @jk1 when you said *It scales in a vertical manner and is quite good at it.* do you have an idea how YT is good at vertical scaling and how the *race condition* you mentioned affects YT? – quarks Jan 03 '21 at 09:34
  • @quarks YouTrack has no known race condition issues at the moment. It was meant to be an example of a random custom code bug. As for the scalability, you may refer to youtrack.jetbrains.com as an example. It holds 2M issues, 4.5M comments and serves about 10K active user sessions. – Jk1 Jan 05 '21 at 11:44
  • 10K active connections, that server must be huge? – quarks Jan 05 '21 at 16:00