Cache hit ratio below optimal causes excessive disk I/O

Low buffer cache hit ratio indicates queries are reading from disk instead of memory, causing performance degradation due to increased I/O operations.

Monitor cache hit ratios using postgres_exporter metrics. Calculate hit ratio from blks_hit and blks_read in pg_stat_database. If consistently below 95-99%, consider increasing shared_buffers. Review query patterns and add indexes to reduce full table scans.