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Use

<number of> physical reads for user task <task_ID>, <number of> commands, application pid <pid>


Explanation

The user task <task_id> causes a large number of physical reads to take place on the volumes of the database, because the data requested by the applications was not found in the data cache.


User Response

If a table is accessed for the first time, or if it has not been used for a long time, and was therefore displaced from the data cache, then this situation is not a problem.

However, if this does not explain the read activity, you should check the hit rate for the data cache, and increase the size of the data cache, if necessary.

Make sure that the SQL statements specified by the application do not read significantly more data than is necessary for processing, because of poor                                                                          search strategies, for example.

If the special database parameter UseDataCacheScanOptimization has the value yes, then table scans ( TABLE SCAN ) use only 10% of the data cache for caching the table. This means that it may not be possible to hold the entire table in the data cache, and the next scan has to read it physically again.

 

More Information

Relevant  DB-Analyzer Files
Helpful with ...
DBAN_CACHES.csv Successful and unsuccessful accesses to caches, and also hit rates 
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 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.
Session 26: SAP MaxDB I/O Concept  
Documentation (links)
Helpful with ...

Concepts of the Database System
Working Memory Areas

<übernommen> 
SQL Optimizer
Search Strategies
 

Database Administration
Special Database Parameters

 
TABLE SCAN 
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