create outline ol3732308613_tmp for category GOOD_PLAN on
select /*+ index(a,a_idx) */ … from a;

生成outline后,explain plan select /*+ index(a,a_idx) */ … from a; 却发现没有走a_idx,而是选择了full table scan

我看了一下ol$hints表,发现其并没有使用index hint,而是使用了INDEX_RS_ASC,并且还有一个hint为OPTIMIZER_FEATURES_ENABLE(‘9.2.0′)


在创建outline前加上alter session set optimizer_features_enable=’′ 就可以了


about INDEX_RS_ASC (from jonathanlewis’s blog)

Bonus: The index() hint tell Oracle to use an index, but does not specify whether that the usage should be a full scan or a range scan. Because of some changes in costing in 10g, there have been cases reported where the optimizer – after hinting – picked a full scan when a range scan would have been a more intelligent choice. Consequently Oracle Corp. has introduced three new hints in to “disambiguate” the index use. These are: index_rs(), index_rs_asc(), index_rs_desc(), which make explicit demands for an index range scan. It’s probably a good idea to use this option in all future code.

122 thoughts on “Outline不能正确使用的问题

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