Table scans

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

Explanation

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.