Cache hit ratio below 99% indicates insufficient shared_buffers memory

Cache hit ratio (percentage of data blocks served from memory vs disk) drops below 99%. Indicates shared_buffers insufficient for working set — frequent disk I/O degrades query performance. Buffer reads from disk become dominant factor in query execution time.

Monitor cache hit ratio continuously — should remain >99%. If consistently lower, increase shared_buffers allocation. Review EXPLAIN ANALYZE output for 'Buffers: shared read' — high values indicate cache misses requiring disk I/O. Increase RAM allocation or optimize queries to reduce working set size.