FM3 — Unbounded Resource Consumption
BFS stores the entire frontier in memory. On a graph with high out-degree (web pages with hundreds of links, social graphs with high-follower accounts), the frontier grows rapidly. A BFS from a popular page can add millions of URLs to the frontier in the first few levels. Production crawlers cap frontier size and use disk-backed queues.
FM11 — Observability Blindness
A cycle in a dependency graph that is not detected will cause infinite recursion in DFS (stack overflow in most languages). The classic symptom is a dependency resolution command that hangs or crashes with a stack overflow rather than a clear error message. The fix is the two-set cycle detection shown above. The failure is nearly always from a dependency graph that includes a two-package mutual dependency that was introduced by a version upgrade.