The buffer pool hit ratio for a database. This is ratio of physical reads to logical reads for the database, expressed as a percentage. It is a measure of how often reads are made from pages that are already in a buffer pool compared to how often they are made from pages that must be loaded from disk. A higher percentage indicates more data is being read from the buffer pool. This means a lower frequency of disk I/O. A lower percentage means more data is being read from disk. This means a higher frequency of disk I/O and slower performance.