POSTGRESQL CDC BACKFILLS AT SCALE: RUNNING A MULTI-DAY BACKFILL WHILE PRODUCTION KEEPS WRITING

Summary from the TLDR Data newsletter

Large PostgreSQL CDC backfills fail less from historical reads than from WAL retention, delayed slot acknowledgments, long-running transactions, and stale snapshot rows racing live changes. Safer designs keep consuming WAL during chunked reads, checkpoint progress, reconcile overlaps with watermarks and fences, and size chunking around real write rates.