Universally Unique Identifiers (UUIDs) are great. I love how you can tell the progress of a batch job just by looking at the current UUID. If it starts with 0... , the task is less than 1/16th done. If it starts with 7d.. , we're almost halfway there. At ff... we are nearing the end. The fact that you can tell this rests on two principles: 1) you sort your jobs by their uuid and 2) UUIDs are random, as in, distributed uniformly . However, last week, I noticed a strange thing: a clearly visible pattern in the uuid column of a database table. It should be impossible, but there it was. It looked like this: > SELECT uuid FROM example ORDER BY id; 4f95de28-0fd1-48db-ad2e-34ecd169c483 4331cb9e-1d91-11e9-be2c-45923c63e8a2 4331cc4c-1d91-11e9-be2c-45923c63e8a2 4331ccec-1d91-11e9-be2c-45923c63e8a2 4331cd7e-1d91-11e9-be2c-45923c63e8a2 c7e2f124-f6ba-4434-843f-89958a7436ec 4331ce10-1d91-11e9-be2c-45923c63e8a2 4331ce9e-1d91-11e9-be2c-45923c63e8a2 4331cf28-1d91-11e9-be2c-45923c