Optimizer Strategies 

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

Explanation

The ratio of read table rows to found table rows is poor when a particular access strategy (<optimizer_strategy_executes>) is used.

The access strategy can be one of the following strategies:

·        Primary key accesses
(EQUAL CONDITION FOR KEY,
SUBQ CONDITION FOR KEY,
IN CONDITION FOR KEY)

·        Primary key range accesses
(RANGE CONDITION FOR KEY,
SUBQ CONDITION FOR KEY,
IN CONDITION FOR KEY)

·        Index accesses
(EQUAL CONDITION FOR INDEX,
SUBQ CONDITION FOR INDEX,
IN CONDITION FOR INDEX)

·        Index range accesses
(RANGE CONDITION FOR INDEX,
SUBQ CONDITION FOR INDEX,
IN CONDITION FOR INDEX)

·        Isolated index accesses
see: EXPLAIN statement: O,D,T,M Columns, column O (Only Index)
and Index accesses

·        Isolated index range accesses
see: EXPLAIN statement: O,D,T,M columns, column O (Only Index)
and Index range accesses

·        Isolated index scans
(INDEX SCAN)

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.

See also: Table scans