Case: One 2.1M-URL sitemap → 43 split files

Case: One 2.1M-URL sitemap → 43 split files
A marketplace served every URL in a single gzipped sitemap. Google read it once every 9 days.
What we did:
— Split into 43 files at 50,000 URLs each, wrapped in one index
— Grouped by section so each file maps to one content type
— Set per-section lastmod from the DB, not deploy time
Measured outcome over 6 weeks:
— Average crawl interval per file dropped 9 days → 31 hours
— Indexed URLs rose from 71% → 94%
Checklist to copy:
✅ Max 50,000 URLs per file
✅ Max 50MB uncompressed per file
✅ One index referencing every child
✅ Each file scoped to a single section
Definition of done: no single file exceeds either limit and the index lists all children.