Data cache hitrate (SQL Pages) <percentage>%, <number> of <number> accesses failed
The hit rate when accessing the data cache is too low. The hit rate in a running SAP 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 UseDataCacheScanOptimization has the value yes). Data cache hit rates that are lower than 99% over a fifteen-minute average must be avoided.
Check the following points:
- The data cache load
- The configuration of the database instance and the hardware
- In SAP liveCache databases, 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.
Relevant DB-Analyzer Files
Helpful with ...
|DBAN_CACHES.csv||Successful and unsuccessful accesses to caches, and also hit rates|
|SAP Note||Helpful with ...|
Expert Sessions (Link to trainings)
Content / Helpful with ...
|Session 16: SAP MaxDB SQL Query Optimization (Part 1) |
Session 16: SAP MaxDB SQL Query Optimization (Part 2)
|Find detailed information about different optimizer strategies and performance optimization.|
Helpful with ...
Concepts of the Database SystemWorking Memory Areas