## Data Cache Hit Rate

Data cache hit rate <percentage>%, <number> of <number> accesses failed

### Explanation

The hit rate when accessing the data cache is too low. The hit rate in a running liveCache application should not be under 100%.

Lower hit rates may occur for short periods of time, for example, when objects are accessed for the first time, or if a table that is being scanned (TABLE SCAN) is larger than 10% of the data cache (only if the special database parameter LRU_FOR_SCAN has the value yes). Data cache hit rates that are lower than 99% over a fifteen-minute average must be avoided.

### User Response

Check the following points:

· The data cache load

· The configuration of the database instance and the hardware

· In liveCache instances, the size of the plan versions, as well as OMS versions that have existed for a long time.

Frequently, individual SQL statements cause a high percentage of the total logical and physical read activity. Increasing the cache just moves the load from the hard disk to the CPU, even though, for example, an additional index could turn a read-intensive table scan into a quick direct access. For information on creating optimized SQL statements, see SQL Optimizer.