Lambda and Kappa

1. The Incident

The store now has two pipelines. The nightly batch computes the authoritative reports. The streaming pipeline feeds the live dashboard. Both compute revenue. On Wednesday morning, finance notices that they disagree. The dashboard's Tuesday total reads $412,880. The batch report says $413,205.

Which one is right? Both, by their own rules. The streaming job dropped some late events. That was its watermark policy, working as designed