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<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: Columns O,D,T,M, column O (Only Index) as well as Index accesses

  • Isolated index range accesses see: EXPLAIN statement: Columns O,D,T,M, column O (Only Index) as well as 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.

Note Note

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

See also: TABLE SCAN

End of the note.

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