How I ran my old RRDtool logger and its SQLite replacement in parallel for months — why you tee the reads instead of double-polling, and how to set a real cutover test before a monitoring-system migration.
How I migrated a two-year RRDtool logging setup to SQLite in WAL mode on a Raspberry Pi 4 — rescued 145,742 legacy rows, kept every historical data point, and used a parallel-run cutover to verify.