duplicate key value violates unique constraint "jobs_job_name_key"

[seamusabshere]

error inserting job caused by: duplicate key value violates unique constraint "jobs_job_name_key"

[emk]

I looked at the code very closely, and I was initially baffled by this. Every place that creates jobs uses unique_kubernetes_job_name, which calls resource_tag and ThreadRng to generate a unique job suffix. And ThreadRng uses a cryptographic seed that supposedly uses kernel entropy.

But then I realized that we imitate the way that Kubernetes uses 5-character tags, which gives us only 36^5 = 60,466,176 possible tags.

Which means that after an estimated sqrt(36^5) = 7,776 jobs, we got bit by the Birthday paradox. Oops. Fortunately, this is an easy fix.