[orf]

None of that matters: what is your application going to do if it tries to allocate 3mb of data from your 2mb allocator?

This is the far more meaningful part of the original comment:

> and furthermore most code is not in a position to do anything other than crash in an OOM scenario

Given that (unlike a language such as Zig) Rust doesn’t use a variety of different allocator types within a given system, choosing to reliably panic with a reasonable message and stack/trace is a very reasonable mindset to have.

[ncruces]

Since we're talking about SQLite, by far the most memory it allocates is for the page cache.

If some allocation fails, the error bubbles up until a safe place, where some pages can be dropped from the cache, and the operation that failed can be tried again.

All this requires is that bubbling up this specific error condition doesn't allocate. Which SQLite purportedly tests.

I'll note that this is not entirely dissimilar to a system where an allocation that can't be immediately satisfied triggers a full garbage collection cycle before an OOM is raised (and where some data might be held through soft/weak pointers and dropped under pressure), just implemented in library code.

[orf]

Sure, and this is completely sensible to do in a library.

But that’s not the point: what can most applications do when SQLite tells them that it encountered a memory error and couldn’t complete the transaction?

Abort and report an error to the user. In a CLI this would be a panic/abort, and in a service that would usually be implemented as a panic handler (which also catches other errors) that attempts to return an error response.

In this context, who cares if it’s an OOM error or another fatal exception? The outcome is the same.

Of course that’s not universal, but it covers 99% of use cases.

[osiris88]

In C++ it will throw an exception which you can catch, and then gracefully report that the operation exceeded limits and/or perform some fallback.

Historically, a lot of C code fails to handle memory allocation failure properly because checking malloc etc for null result is too much work — C code tends to calm that a lot.

Bjarne Stroustrup added exceptions to C++ in part so that you could write programs that easily recover when memory allocation fails - that was the original motivation for exceptions.

In this one way, rust is a step backwards towards C. I hope that rust comes up with a better story around this, because in some applications it does matter.