When a site has hundreds of URL changes.
WHEN THIS ARISES
A redesign changing URL structure A domain change Consolidating several sites Removing a large section
THE APPROACHES
Individual rules in .htaccess, which is fine up to a few dozen Pattern-based rules, where the old and new structures relate predictably A redirect plugin or application-level handling, which scales better and is easier to manage A mapping file, for large one-to-one sets
PERFORMANCE
Hundreds of individual .htaccess rules are evaluated on every request, including for URLs that do not need redirecting. Use patterns where possible, or handle it in the application.
PRIORITY
Redirect the URLs that matter: those with traffic, those with inbound links, and those ranking in search.
Export your current URLs from analytics and search console to find them.
AVOID CHAINS
Each redirect costs a round trip. Redirect directly to the final destination rather than through intermediate steps.
TESTING
A redirect checking tool run against a list of old URLs confirms each reaches the right destination in one hop.
AFTERWARDS
Monitor 404s for a month. Anything appearing was missed.