Use
Avg read time <duration> ms for <number_of> reads on volume <volume_name>
Explanation
Generally in a tuned system data mainly should be read from the caches. Nevertheless, for some actions physical I/O is sometimes unavoidable. If it is necessary, the times for read I/O should not be higher than 10 ms for modern disks, usually smaller than 5 ms, if a lot of read operations are done.
Currently you will often find high priority warnings related to just a few read operations. If there is a high duration for just a few reads, it is usually not critical.
User Response
If you observe high read times related to a high amount of I/O you should check the disk architecture. Additionally a performance analysis could be helpful to check if unnessary physical I/O is caused by wrong optimizer strategies because of disadvantageous access paths.
More Information
| Relevant DB-Analyzer Files | Helpful with ... |
|---|---|
| DBAN_IO.csv | Read and write operations to cache pages and data pages |
| DBAN_IOTHREADS.csv | Number and duration of physical write and read operations (I/O threads) |
| SAP Notes | |
|---|---|
| Expert Sessions | Content / Helpful with ... |
|---|---|
| Session 26: SAP MaxDB I/O Concept | |
| 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. |
| Documentation (links) | |
|---|---|
| Optimizer Search Strategies |