[throwaway894345]

Yes, but you have to go out of your way when writing software to make it so the software can only run on one node at a time. Or rather, well-architected software should require minimal, isolated edits to run in a distributed configuration (for example, replacing SQLite with a distributed SQLite).

[thayne]

That's just not true. Distributed software is much more complicated and difficult than non-distributed software. Distributed systems have many failure modes that you don't have to worry about in non-distributed systems.

Now maybe you could have an abstraction layer over your storage layer that supports multiple data stores, including a distributed one. But that comes with tradeoffs, like being limited to the least common denominator of features of the data stores, and having to implement the abstraction layer for multiple data stores.

[throwaway894345]

I’m a distributed systems architect. I design, build, and operate distributed systems.

> Distributed systems have many failure modes that you don't have to worry about in non-distributed systems.

Yes, but as previously mentioned, those failure modes are handled by abiding a few simple principles. It’s also worth noting that multiprocess or multithreaded software have many of the same failure modes, including the one discussed in this post. Architecting systems as though they are distributed largely takes care of those failure modes as well, making even single-node software like Jellyfin more robust.

> Now maybe you could have an abstraction layer over your storage layer that supports multiple data stores, including a distributed one. But that comes with tradeoffs, like being limited to the least common denominator of features of the data stores, and having to implement the abstraction layer for multiple data stores.

Generally I just target storage interfaces that can be easily distributed—things like Postgres (or maybe dqlite?) for SQL databases or an object storage API instead of a filesystem API. If you build a system like it could be distributed one day, you’ll end up with a simpler, more modular system even if you never scale to more than one node (maybe you just want to take advantage of parallelism on your single node, as was the case in this blog post).

[thayne]

> just target storage interfaces that can be easily distributed—things like Postgres

But as I mentioned above, that makes the system more complicated for people who don't need it to be distributed.

Setting up separate db software, configuring the connection, handling separate updates, etc. is a lot more work for most users than Jellyfin just using a local embedded sqlite database. And it would probably make the application code more complicated as well.

[throwaway894345]

> But as I mentioned above, that makes the system more complicated for people who don't need it to be distributed. Setting up separate db software, configuring the connection, handling separate updates, etc. is a lot more work for most users than Jellyfin just using a local embedded sqlite database.

You can package a Postgres database with your app just like SQLite. Users should not have to know that they are using Postgres much less configuring connections, handling updates, etc.

> And it would probably make the application code more complicated as well.

Not at all, this is an article about the hoops the application has to jump through to make SQLite behave well with parallel access. Postgres is designed for parallel access by default. It’s strictly simpler from the perspective of the application.

[thayne]

> You can package a Postgres database with your app just like SQLite

You technically can. But that is much more difficult to do than including sqlite, and isn't how postgresql was meant to be used. And what happens when you want to upgrade the major version of postgresql? Do you now include two versions of postgresql so that you can convert old databases to the new postgresql format? I certainly wouldn't say it is "just like SQLite".

[throwaway894345]

I can believe the packaging step is more difficult on some platforms, but that’s a one time cost per platform.

Upgrades are more complex because Postgres (for some reason) doesn’t endure backwards compatibility with its disk format like sqlite across major versions (minor versions work fine though). For major version upgrades you ship both binaries and use pg_upgrade or pg_dump/pg_restore. It’s annoying, but it’s a one time cost to automate. It’s not like battling concurrency bugs in sqlite.