Postgres recovery_prefetch can cause outages

PostgreSQL's `recovery_prefetch` feature, introduced to improve WAL recovery performance, has been causing production outages in real-world deployments. The issue occurs when the prefetch mechanism issues unnecessary I/O requests for data blocks that are already present in shared buffers via Full Page Writes (FPW), leading to excessive kernel-space CPU usage and significant replay lag on standby servers. The problem was flagged during development in 2021 but dismissed as not critical enough to address before the feature shipped.