Description: Cache Hit Ratio scaled by 100. Measures the effectiveness of the hits against the buffer cache. Whenever Oracle reads data from disk, it places that data into the buffer cache. Data is aged out of the buffer cache using a least recently used algorithm. Oracle looks in the buffer cache first for data requests. If the data is not there, Oracle searches the disk based data files that comprise the database. On most production systems, Oracle should not have to resort to disk reads more than 20% of the time. So, if the buffer cache hit ratio is less than 80%, you should consider increasing the database buffer cache in the System Global Area. This can be done by increasing the value for DBBLOCKBUFFER in the initialization parameter file.