Users should not be able to file exact duplicate requests

[bardiharborow]

See #235483.

[stwalkerster]

Typical INSERT-based race condition between two transactions in two threads.

We already run in serializable isolation mode, and a unique index is not going to work from a business logic point of view. Locks might be the only available way forward, but I'm not keen on applying locks to that table.

[bardiharborow]

Perhaps we could go way more low-tech with this one, and just add onclick="this.disabled = true; this.value = "Submitting...";" to the submit button?

[stwalkerster]

We shouldn't rely an JavaScript being available on the public side - there's still a good number of screen readers which don't support it.

It might help with some instances of this issue (how many would need analysis of webserver logs), but it's not a complete solution.

I'd prefer a more structural solution which works for all instances of this, as I expect there are many instances of this issue in many places across the tool.