Every Salesforce team hits the same wall eventually. A business stakeholder walks over and says: "We need to update the Region__c field on 2.3 million Account records based on a new territory model." Someone opens Data Loader, exports a CSV, runs a VLOOKUP in Excel, and re-imports. It takes a full afternoon. Two weeks later, the territory model changes again.
There's a better way. Batch Apex lets you encode the logic of that update - not just the data - so it's repeatable, testable, auditable, and parameterized for the next time it happens. This article covers how to design batch classes that are genuinely reusable across backfill scenarios, the trade-offs you need to understand before choosing this approach, and how to monitor jobs once they're running.
The Anatomy of a Batch Class (Quick Refresher)
If you've written Batch Apex before, skim this section. If not, here's the contract you're implementing:
public class AccountRegionBackfill implements Database.Batchable {
