Frequent errors when clicking on crate Dependents link about crates.io

[Turbo87]

unfortunately this is caused by a performance issue with the corresponding database query. on less depended-upon crates it works fine but for cases like werde it takes a long time to respond. some attempts have been made to improve the situation, but it's still very slow unfortunately.

[qarmin]

Serde have 33840 reverse dependencies, so I think that this is expected.

But I have sometimes problem with printpdf, which have only 20 reverse dependencies, which is more strange - https://crates.io/crates/printpdf/reverse_dependencies

[osa1]

I've encountered the same issue in https://crates.io/crates/salsa/reverse_dependencies.

This package only has 34 reverse dependencies.

Refreshing the page a few times worked.

[CAD97]

Mainly just recording/calling out that it's reporting 500 internal error, and a change to report a timeout instead (if that's indeed what's ocurring) would be nice and less work than actually addressing the issue. (Turbo admitted overlooking that on Zulip.)

The fix would probably be a caching/invalidation layer around frequent/expensive rdep queries. Which certainly isn't trivial to be fair, but also probably any query that doesn't need to reflect registry updates immediately to be useful will likely end up wanting such a layer as the registry grows.

Errors even with a low count of rdeps don't seem too strange, since if it's a performance issue, load can probably impact adjacent queries' performance/success as well.