Low buffer hit ratio indicates insufficient shared_buffers or cache pressure

Buffer hit ratio below 99% indicates excessive disk reads. Shared_buffers too small or working set exceeds available cache. Each cache miss requires physical I/O, degrading query performance.

Check buffer hit ratio via query: sum(blks_hit) * 100.0 / sum(blks_hit + blks_read) from pg_stat_database. If below 99%, increase shared_buffers (recommended 25% RAM, max 40%). Monitor per-table hit ratios to identify hot tables. Verify effective_cache_size matches available OS cache.