| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Buffer_cache_hit_ratio |
The percentage of time the database server is able to satisfy a request directly from the cache |
Percent
|
Physical I/O takes significant amount of time and also increases CPU resources required. The database configuration should be tuned to ensure that a required block will be most likely in memory. The extent to which this is achieved is measured using this measure. Ratio should be 80% or higher. A lower value indicates insufficient memory allocation to the database buffer cache. |
| Library_cache_hit_ratio |
Library cache is a buffer that contains the shared SQL and PL/SQL areas. The library cache hit ratio indicates the percentage of shared SQL statements being reparsed. |
Percent
|
For a well-tuned database, this ratio is 90%. A lower hit ratio may indicate that the memory allocation to the library cache is insufficient. A low value can degrade the database performance. |
| Redo_log_buffer_entries |
The number of entries in the redo log buffer describing changes made to the database |
Number
|
The changes made to the database are first written to the redo log buffer. The database then periodically writes batches of the redo entries to the online redo log files. The lesser the number of entries in the Redo Buffer, the lesser the database changes are reflected in the buffer. Therefore, there will be higher disk reads and system performance will decrease.
|