The kind of application files they are talking about (things like word processor documents, spreadsheets, drawings, source code control system data) would only be writing sporadically. During one of those sporadic writes they might need to update thousands of rows but those could all be done in one transaction.

Reference: https://www.sqlite.org/faq.html, question 19. (I've seen similar when testing on SSDs locally).

It has generally become much better in the last decade or two, but one should still expect most OS's to sometimes pause for excessive amounts of time on disk IO unless the API is specifically guaranteed to never pause. Even then one would be wise to measure/log deviations if it's critical for the application. OS guarantees might also be contingent on driver/subsystem guarantees, and bad drivers might sometimes affect what seems completely unrelated upstream systems.

Yes, and other file formats encourage doing things in memory, so you don't have any disk i/o in the common path.

Using sqlite as a file format strongly discourages the simple, jank-free until you press save workflow of slurping your content, operating on it in memory, and then outputting it all in one operation as a response to an explicit user action. Instead, your whole application gets small but perceptible delays across all operations and interactions.

It's not "their" experience report.

And to be clear: this will still be user-visible with literally any other file format. The slow part ain't SQLite itself; it's the disk to which you're writing.

Doesn't this apply to writing files in general? It's not unique to SQLite...

Edit: Nope, SQLite is designed to be protected against crashes, even OS crashes.

Are you talking about a server application?

> or unsafe if you find for performance (you can get it up to, IIRC, ~50k transactions per second, but if your program or computer dies half way, your file is hosed)

Never heard that SQLite has unsafe operations. Any source?

I'm talking about doing a handful of transactions -- even a single one, now that I looked at the actual numbers that sqlite discusses -- being enough to introduce user-visible jank.

> Never heard that SQLite has unsafe operations. Any source?

The sqlite docs. You can improve the performance of sqlite by multiple orders of magnitude by messing with things like https://www.sqlite.org/pragma.html#pragma_synchronous, at the cost of safe atomic updates.

Thanks for the link, but only when the OS or your computer crashes, not even the application itself. Could you introduce any application file format that is safe in that case? Obviously your JSON file format is much more unsafe than that, not to mention the huge overhead of JSON with binary data.

Ah, right there are also the journalling knobs that you'd tweak to get to max performance -- either in-memory or no journalling at all make a big impact. There are a bunch of them scattered throughout the docs.

> Could you introduce any application file format that is safe in that case? Obviously your JSON file format is much more unsafe than that, not to mention the huge overhead of JSON with binary data.

Yes, any format is safe if you write to a temporary file, and then rename(2) it to replace it. This is guaranteed to be atomic, so it works with anything (including sqlite, though at that point all sqlite does is cost you performance and complexity).

Huh?

I was pushing updates to a SQLite file on my laptop a few weeks ago with code that's not at all optimised, and wasn't too fussed with ~400 transactions a second, sustained for a minute or so.

What were you doing that only gave 10 transactions a second?