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<number of> table scans, selectivity <percentage>%: <number of> rows read, <number of> rows qualified


 The ratio of read rows to found rows is poor for table scans ( TABLE SCAN ). This often indicates a poor search strategy, caused either by the application (missing or insufficient indexes), or by a problem in the SELECT optimization of the database kernel.

Scanning large tables can have seriously negative effects on the performance of the entire system.

User Response

Find the statement that causes this poor ratio of read rows to found rows, and check the access strategies for this statement.


For information on creating optimized SQL statements, see the SQL Optimizer documentation.


More Information

Relevant  DB-Analyzer Files
Helpful with ...
DBAN_STRATEGY_SCANS.csvAccesses and selectivity for INDEX SCAN and TABLE SCAN searches
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
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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 ...
SQL Optimizer Search Strategies 
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