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Use

Number of physical writes: <number_of> pages, avg. <number_of> pages per second


Explanation

Not all of the data used by the applications can be held in the data cache. This causes pages from the data cache to be displaced to the data area, which means that there is a large number of writes to the data volumes.

This phenomenon is almost unavoidable if load times (data import) are long, because the imported data is usually much larger than the size of the data cache.

A savepoint also writes modified pages from the data cache to the data area at regular intervals. Read and write activity increases significantly at this time, without causing a genuine bottleneck. In normal operations, you should not be able to measure any significant write activities other than the savepoints.


User Response

If you notice a high level of write activity in normal operations, first make sure that no savepoint was active during the measurement interval (which is possibly too short).

If no savepoint was active, increase the size of the data cache.

 

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

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