"type": "skip_scan", "index": "PRIMARY", "key_parts_used_for_access": [ "f1", "f2" ], "range": [ "40 < f2" ], "chosen": true }, 我们从innodb的角度来看看这个SQL是如何执行的,我们知道每个index scan都会走到ha_innobase::index_read来构建search tuple,上述查询的执行步骤: 第一次...
也可以从optimizer trace里看到如何选择的skip scan: "skip_scan_range":{"potential_skip_scan_indexes":[{"index":"PRIMARY","tree_travel_cost":0.4,"num_groups":3,"rows":53,"cost":10.625}]},"best_skip_scan_summary":{"type":"skip_scan","index":"PRIMARY","key_parts_used_for_access":[...
"skip_scan_range": {"potential_skip_scan_indexes": [ {"index":"PRIMARY","tree_travel_cost":0.4,"num_groups":3,"rows":53,"cost":10.625} ] },"best_skip_scan_summary": {"type":"skip_scan","index":"PRIMARY","key_parts_used_for_access": ["f1","f2"],"range": ["40 < f2"...
For as long as there have been a range access method in MySQL, the number of rows in a range has been estimated by diving down the index to find the start and end of the range and use these to count the number of rows between them. This technique is accurate, and is therefore a g...
索引跳跃扫描(Index Skip Scan)可以使用到复合索引的非前缀索引列,达到改善性能的作用,前提是全表扫面的代价高于索引跳跃式扫描的代价。这里给出使用HINT方法使SQL走索引跳跃扫描的方法。 1.初始化环境 1)创建表T sec@ora10g> create table t(x number,y number); ...
(0)|00:00:01||1|TABLEACCESSBYINDEXROWID|table_test|1|16|1(0)|00:00:01||*2|INDEXRANGESCAN|table_test_ID_CODE_I|1||1(0)|00:00:01|---PredicateInformation(identifiedbyoperationid):---2-access("CODE"=666666AND"ID"=666666)Statistics---...
Method Android.Text.Style Android.Text.Util Android.Transitions Android.Util Android.Util.Proto Android.Views Android.Views.Accessibility Android.Views.Animations Android.Views.Autofill Android.Views.ContentCapture Android.Views.ContentCaptures Android.Views.DisplayHash Android.Views.InputMethods Android.Views....
3 - access("ID">2750) The optimizer has chosen an index range scan on the (single-column) t1 index. Since this path costs more than the index fast full scan it would appear that the index() hint does not allow the optimizer to consider an index fast full scan. So we might decide...
Excel, error using SaveAs method Exception calling "AddAccessRule" with "1" argument(s): "Some or all identity references could not be transla ted." error Exception calling "ExecuteNonQuery" with "0" argument(s): "The parameterized query 'IN' expects the parameter which was not supplied. ...
Using the judgment criteria of ICCs ≥ 0.80, a total of 2194 features were initially screened (ICC range: 0.80-1.00), with 438 features eliminated (ICC range: 0.75–0.79). The feature pool includes: (i) first-order features; (ii) shape features; (iii) gray-level co-occurrence matrix...