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测试组合索引
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測試背景：生產數據庫的會員表和產品表中存在三個CLOB字段(這些字段主要用來存會員和產品的描述信息)，隨著數據量的增長，全表掃描的時候，I/O等待嚴重，于是想到分表！
提出問題：這兩張大表，加起來的索引總共有35個，其中會員表的索引數為17個，產品表的索引數為18個(35個索引中不包含LOB字段的索引)，這些索引大部分為組合索引，且存在函數索引(函數索引均為組合索引的前導列進行desc排序)
索引優化測試：在測試庫中進行優化測試，原始會員表用test代替，用戶schema用hr代替，數據庫版本為11.2.0.3 32bit on widows2003 enterprise edition
一:建表,添加主鍵約束和組合索引1
SQL>?create?table?t1?as?select?*?from?test; ??SQL>?alter?table?t1?add?constraint?pk_t1_id?primary?key?(id); ?Table?altered. ??SQL>?create?index?idx_t1_mul1?on?t1(status,registersource); ?Index?created.? 二：收集表統計信息,對status字段的空值進行賦值，status字段為會員的狀態，1為正常狀態，其他值均為異常狀態，所以值的分布傾斜
SQL>?update?t1?set?status=0?where?status?is?null; ?4?rows?updated. ??SQL>?commit; ?Commit?complete. ??SQL>?exec?dbms_stats.gather_table_stats(‘HR’,'T1',CASCADE=>true); ?PL/SQL?procedure?successfully?completed. ??SQL>?select?status,count(*)?from?t1?group?by?status; ??????STATUS???COUNT(*) ?----------?---------- ??????????1?????595612 ??????????2???????1230 ??????????4?????????10 ??????????5??????????1 ??????????3???????2746 ??????????0??????26825 ?6?rows?selected.? 三：測試證明結果集比較小的情況下，where字句中包含前導列的時候就會使用組合索引
SQL>?select?id,version?from?t1?where?status=0; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?26939?|???289K|??6051???(1)|00:01:13?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?26939?|???289K|??6051???(1)|00:01:13?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|?26939?|???????|????93???(0)|00:00:02?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=0)? 四：建組合索引2(組合索引2的字段同組合索引1一樣，只是前導列對調)，對registersource字段的空值進行賦值，收集表的統計信息；(該字段用來存儲用戶的注冊來源，值分布也存在傾斜的情況)
SQL>?create?index?idx_t1_mul2?on?t1(registersource,status); ?Index?created. ??SQL>?select?registersource,count(*)?from?t1?group?by?registersource; ??REGIST???COUNT(*) ?------?---------- ?1?????????????156 ?????????????????4 ?3????????????1689 ?6???????????????4 ?0???????????23487 ?2??????????601084 ?6?rows?selected. ??SQL>?update?t1?set?registersource=6?where?registersource?is?null; ?4?rows?updated ??SQL>commit； ?Commit?complete. ??SQL>?exec?dbms_stats.gather_table_stats(‘HR’,'T1',CASCADE=>true); ?PL/SQL?procedure?successfully?completed.? 五：只查詢registersource字段且結果集小的時候，執行計劃采用組合索引2?
SQL>?select??*?from?t1?where?registersource='1';?//這里registersource字段為varchar2類型，故而加引號 ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?2744963562 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|???227?|???287K|????49???(0)|00:00:01?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|???227?|???287K|????49???(0)|00:00:01?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL2?|???227?|???????|?????3???(0)|00:00:01?| ?------------------------------------------------------------------------------------------ ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("REGISTERSOURCE"='1')? 六：傾斜組合測試
1：小小 ?SQL>?select?*?from?t1?where?status=0?and?registersource=0; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??1057?|??1337K|???280???(0)|00:00:04?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??1057?|??1337K|???280???(0)|00:00:04?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|??1057?|???????|????68???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=0) ????????filter(TO_NUMBER("REGISTERSOURCE")=0) ??SQL>?select?*?from?t1?where?registersource=0?and?status=0; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??1057?|??1337K|???280???(0)|00:00:04?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??1057?|??1337K|???280???(0)|00:00:04?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|??1057?|???????|????68???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=0) ????????filter(TO_NUMBER("REGISTERSOURCE")=0) ??2:小大 ?SQL>?select?*?from?t1?where?status=0?and?registersource=2; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?28531?|????35M|??5776???(1)|00:01:10?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?28531?|????35M|??5776???(1)|00:01:10?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|?28531?|???????|????68???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=0) ????????filter(TO_NUMBER("REGISTERSOURCE")=2) ??SQL>?select?*?from?t1?where??registersource=2?and?status=0; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|?Time???| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?28531?|????35M|??5776???(1)|00:01:10?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?28531?|????35M|??5776???(1)|00:01:10?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|?28531?|???????|????68???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=0) ????????filter(TO_NUMBER("REGISTERSOURCE")=2) ??3:大小 ?SQL>?select?*?from?t1?where?status=1?and?registersource=0; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1106331959 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?21105?|????26M|??4659???(1)|00:00:56?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?21105?|????26M|??4659???(1)|00:00:56?| ?|*??2?|???INDEX?SKIP?SCAN???????????|?IDX_T1_MUL2?|?21105?|???????|???437???(0)|00:00:06?| ?------------------------------------------------------------------------------------------ ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=1) ????????filter(TO_NUMBER("REGISTERSOURCE")=0?AND?"STATUS"=1) ??SQL>?select?*?from?t1?where??registersource=0?and?status=1; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1106331959 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?21105?|????26M|??4659???(1)|00:00:56?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?21105?|????26M|??4659???(1)|00:00:56?| ?|*??2?|???INDEX?SKIP?SCAN???????????|?IDX_T1_MUL2?|?21105?|???????|???437???(0)|00:00:06?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("STATUS"=1) ????????filter(TO_NUMBER("REGISTERSOURCE")=0?AND?"STATUS"=1) ??4:大大 ?SQL>?select?*?from?t1?where?status=1?and?registersource=2; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?3617692013 ?-------------------------------------------------------------------------- ?|?Id??|?Operation?????????|?Name?|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?-------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT??|??????|???569K|???703M|?32570???(1)|?00:06:31?| ?|*??1?|??TABLE?ACCESS?FULL|?T1???|???569K|???703M|?32570???(1)|?00:06:31?| ?-------------------------------------------------------------------------- ??Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????1?-?filter("STATUS"=1?AND?TO_NUMBER("REGISTERSOURCE")=2) ??SQL>?select?*?from?t1?where??registersource=2?and?status=1; ?Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?3617692013 ?-------------------------------------------------------------------------- ?|?Id??|?Operation?????????|?Name?|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?-------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT??|??????|???569K|???703M|?32570???(1)|?00:06:31?| ?|*??1?|??TABLE?ACCESS?FULL|?T1???|???569K|???703M|?32570???(1)|?00:06:31?| ?-------------------------------------------------------------------------- ??Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????1?-?filter("STATUS"=1?AND?TO_NUMBER("REGISTERSOURCE")=2)? 測試結果表明，cbo將根據結果集的大小來決定使用最優的執行計劃
七：組合索引和其他字段的配合使用(測試結果說明where子句中包含組合索引的前導列，且結果集小的情況下，執行計劃會選擇走組合索引)
SQL>?select?*?from?t1?where?status=0?and?createddate?<?sysdate; ?Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1745128362 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?29698?|????36M|??6009???(1)|00:01:13?| ?|*??1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?29698?|????36M|??6009???(1)|00:01:13?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL1?|?29698?|???????|????68???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ?????1?-?filter("CREATEDDATE"<SYSDATE@!) ????2?-?access("STATUS"=0) ??SQL>?select?*?from?t1?where?registersource='0'?and?createddate?<?sysdate; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?2744963562 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?22302?|????27M|??4514???(1)|00:00:55?| ?|*??1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?22302?|????27M|??4514???(1)|00:00:55?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?IDX_T1_MUL2?|?22302?|???????|????52???(0)|00:00:01?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????1?-?filter("CREATEDDATE"<SYSDATE@!) ????2?-?access("REGISTERSOURCE"='0')? 八：函數索引測試，對orderno,membership.status,featured四個字段建組合索引3，同時orderno字段進行desc排序；對前面4個字段建立普通的組合索引4，這種做法意在測試是否有必要使用函數索引？
SQL>?create?index?idx_t1_mul3?on?t1(orderno?desc,membership,status,featured); ?Index?created. ??SQL>?select?*?from?t1?where?membership=1?and?status=0?order?by?orderno; ?no?rows?selected ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?687259109 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??5940?|??7517K|??3009???(1)|00:00:37?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??5940?|??7517K|??3009???(1)|00:00:37?| ?|*??2?|???INDEX?FULL?SCAN?DESCENDING|?IDX_T1_MUL3?|??5940?|???????|??1825???(1)|00:00:22?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ?????2?-?access("MEMBERSHIP"=1?AND?"STATUS"=0) ????????filter("STATUS"=0?AND?"MEMBERSHIP"=1) ??SQL>?select?*?from?t1?where?membership=1?and?status=0?order?by?orderno?desc; ?no?rows?selected ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?607735922 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??5940?|??7517K|??3009???(1)|00:00:37?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??5940?|??7517K|??3009???(1)|00:00:37?| ?|*??2?|???INDEX?FULL?SCAN???????????|?IDX_T1_MUL3?|??5940?|???????|??1825???(1)|00:00:22?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ?????2?-?access("MEMBERSHIP"=1?AND?"STATUS"=0) ????????filter("STATUS"=0?AND?"MEMBERSHIP"=1) ??SQL>?drop?index?idx_t1_mul3; ?Index?dropped. ??SQL>?create?index?idx_t1_mul4?on?t1(orderno,membership,status,featured); ?Index?created. ??SQL>?select?*?from?t1?where?membership=1?and?status=0?order?by?orderno; ?no?rows?selected ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?3155127807 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??5940?|??7517K|??1923???(1)|00:00:24?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??5940?|??7517K|??1923???(1)|00:00:24?| ?|*??2?|???INDEX?SKIP?SCAN???????????|?IDX_T1_MUL4?|??5940?|???????|???739???(0)|00:00:09?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("MEMBERSHIP"=1?AND?"STATUS"=0) ????????filter("STATUS"=0?AND?"MEMBERSHIP"=1) ??SQL>?select?*?from?t1?where?membership=1?and?status=0?order?by?orderno?desc; ?no?rows?selected ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?893632694 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|??5940?|??7517K|??1923???(1)|00:00:24?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|??5940?|??7517K|??1923???(1)|00:00:24?| ?|*??2?|???INDEX?SKIP?SCAN?DESCENDING|?IDX_T1_MUL4?|??5940?|???????|???739???(0)|00:00:09?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("MEMBERSHIP"=1?AND?"STATUS"=0) ????????filter("STATUS"=0?AND?"MEMBERSHIP"=1)? 從測試結果上看，不使用函數索引的效果較優，同時去掉這類的函數索引，會方便今后的shrink table操作
九：不使用前導列情況下，組合索引是否能正常使用？在前面測試函數索引的過程中，where條件中不含前導列，只是對結果集進行排序的時候使用前導列，執行計劃選擇組合索引，因而進行如下測試！
SQL>?create?index?idx_t1_mul5?on?t1(password,signinid); ?Index?created. ??SQL>?select?*?from?(select?signinid,count(*)?from?t1?group?by?signinid)?where?rownum<10; ??SIGNINID???????????????????????????????????????????????????????COUNT(*) ?------------------------------------------------------------?---------- ?000000yu??????????????????????????????????????????????????????????????1 ?0000410265269?????????????????????????????????????????????????????????1 ?00006789??????????????????????????????????????????????????????????????1 ?00009746??????????????????????????????????????????????????????????????1 ?000113????????????????????????????????????????????????????????????????1 ?0001mwm???????????????????????????????????????????????????????????????1 ?0002081???????????????????????????????????????????????????????????????1 ?000317????????????????????????????????????????????????????????????????1 ?00032156688???????????????????????????????????????????????????????????1 ??9?rows?selected. ??SQL>?select?*?from?t1?where?signinid='000000yu'; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?2246799375 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?????1?|??1296?|??3706???(1)|00:00:45?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?????1?|??1296?|??3706???(1)|00:00:45?| ?|*??2?|???INDEX?SKIP?SCAN???????????|?IDX_T1_MUL5?|?????1?|???????|??3705???(1)|00:00:45?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ?????2?-?access("SIGNINID"='000000yu') ????????filter("SIGNINID"='000000yu') ??SQL>?select?*?from?t1?where?createddate?<?sysdate?and?signinid='000000yu'; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?2246799375 ?------------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name????????|?Rows??|?Bytes?|?Cost?(%CPU)|Time?????| ?------------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|?????????????|?????1?|??1296?|??3706???(1)|00:00:45?| ?|*??1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1??????????|?????1?|??1296?|??3706???(1)|00:00:45?| ?|*??2?|???INDEX?SKIP?SCAN???????????|?IDX_T1_MUL5?|?????1?|???????|??3705???(1)|00:00:45?| ?------------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ?????1?-?filter("CREATEDDATE"<SYSDATE@!) ????2?-?access("SIGNINID"='000000yu') ????????filter("SIGNINID"='000000yu')? 從測試結果上看，11.2.0.3版本的數據庫，只要查詢語句中包含組合索引的字段，且結果集較小的情況下，執行計劃會選擇組合索引！
十：在10.2.0.1版本的oracle上進行同樣的測試，發現where子句中不出現組合索引的前導列的時候，執行計劃不會選擇組合索引！
(第9和第10的測試有點疑問，后期將繼續測試，ref? http://t.askmaclean.com/viewthread.php?tid=1384&pid=7258&page=1&extra=page%3D1)
SQL>?create?user?test??identified?by?test; ?User?created. ??SQL>?grant?connect,resource,select_catalog_role?to?test; ?Grant?succeeded. ??SQL>?conn?test/test ?Connected. ??SQL>?create?table?t1?as?select?*?from?dba_objects; ?Table?created. ??SQL>?create?table?t1?as?select?*?from?dba_objects; ?Table?created. ??SQL>?desc?t1; ??Name??????????????????????????????????????Null?????Type ??-----------------------------------------?--------?---------------------------- ??OWNER??????????????????????????????????????????????VARCHAR2(30) ??OBJECT_NAME????????????????????????????????????????VARCHAR2(128) ??SUBOBJECT_NAME?????????????????????????????????????VARCHAR2(30) ??OBJECT_ID??????????????????????????????????????????NUMBER ??DATA_OBJECT_ID?????????????????????????????????????NUMBER ??OBJECT_TYPE????????????????????????????????????????VARCHAR2(19) ??CREATED????????????????????????????????????????????DATE ??LAST_DDL_TIME??????????????????????????????????????DATE ??TIMESTAMP??????????????????????????????????????????VARCHAR2(19) ??STATUS?????????????????????????????????????????????VARCHAR2(7) ??TEMPORARY??????????????????????????????????????????VARCHAR2(1) ??GENERATED??????????????????????????????????????????VARCHAR2(1) ??SECONDARY??????????????????????????????????????????VARCHAR2(1) ??SQL>?create?index?i_t1_mul1?on?t1(object_id,object_type); ?Index?created. ??SQL>?set?autot?traceonly?exp ?SQL>?select?*?from?t1?where?object_id?<?100; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?1186876071 ?----------------------------------------------------------------------------------------- ?|?Id??|?Operation???????????????????|?Name??????|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?----------------------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT????????????|???????????|????98?|?17346?|?????4???(0)|?00:00:01?| ?|???1?|??TABLE?ACCESS?BY?INDEX?ROWID|?T1????????|????98?|?17346?|?????4???(0)|?00:00:01?| ?|*??2?|???INDEX?RANGE?SCAN??????????|?I_T1_MUL1?|????98?|???????|?????2???(0)|?00:00:01?| ?----------------------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????2?-?access("OBJECT_ID"<100) ??Note ?----- ????-?dynamic?sampling?used?for?this?statement ???SQL>?select?*?from?t1?where?object_type='INDEX'; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?3617692013 ?-------------------------------------------------------------------------- ?|?Id??|?Operation?????????|?Name?|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?-------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT??|??????|???531?|?93987?|???159???(2)|?00:00:02?| ?|*??1?|??TABLE?ACCESS?FULL|?T1???|???531?|?93987?|???159???(2)|?00:00:02?| ?-------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????1?-?filter("OBJECT_TYPE"='INDEX') ??Note ?----- ????-?dynamic?sampling?used?for?this?statement ???SQL>?set?autot?off ?SQL>?select?count(*)?from?t1; ????COUNT(*) ?---------- ??????50380 ??SQL>?select?object_type,count(*)?from?t1??group?by?object_type; ??OBJECT_TYPE???????????COUNT(*) ?-------------------?---------- ?CONSUMER?GROUP???????????????5 ?INDEX?PARTITION????????????276 ?SEQUENCE???????????????????143 ?QUEUE???????????????????????27 ?SCHEDULE?????????????????????1 ?TABLE?PARTITION????????????128 ?RULE?????????????????????????4 ?JAVA?DATA??????????????????306 ?PROCEDURE???????????????????85 ?OPERATOR????????????????????57 ?LOB?PARTITION????????????????1 ??OBJECT_TYPE???????????COUNT(*) ?-------------------?---------- ?WINDOW???????????????????????2 ?LOB????????????????????????566 ?PACKAGE????????????????????848 ?PACKAGE?BODY???????????????791 ?LIBRARY????????????????????150 ?RULE?SET????????????????????19 ?PROGRAM?????????????????????12 ?TYPE?BODY??????????????????173 ?CONTEXT??????????????????????5 ?JAVA?RESOURCE??????????????770 ?XML?SCHEMA??????????????????26 ??OBJECT_TYPE???????????COUNT(*) ?-------------------?---------- ?TRIGGER????????????????????171 ?JOB?CLASS????????????????????2 ?UNDEFINED????????????????????6 ?DIRECTORY????????????????????9 ?DIMENSION????????????????????5 ?MATERIALIZED?VIEW????????????2 ?TABLE?????????????????????1636 ?INDEX?????????????????????1800 ?SYNONYM??????????????????20026 ?VIEW??????????????????????3671 ?FUNCTION???????????????????270 ??OBJECT_TYPE???????????COUNT(*) ?-------------------?---------- ?WINDOW?GROUP?????????????????1 ?JAVA?CLASS???????????????16417 ?INDEXTYPE???????????????????10 ?CLUSTER?????????????????????10 ?TYPE??????????????????????1926 ?RESOURCE?PLAN????????????????3 ?EVALUATION?CONTEXT??????????14 ?JOB??????????????????????????6 ?41?rows?selected. ??SQL>?set?autot?traceonly?exp ?SQL>?select?/*+index(i_t1_mul1)*/?*?from?t1?where?object_type='INDEX'; ??Execution?Plan ?---------------------------------------------------------- ?Plan?hash?value:?3617692013 ?-------------------------------------------------------------------------- ?|?Id??|?Operation?????????|?Name?|?Rows??|?Bytes?|?Cost?(%CPU)|?Time?????| ?-------------------------------------------------------------------------- ?|???0?|?SELECT?STATEMENT??|??????|???531?|?93987?|???159???(2)|?00:00:02?| ?|*??1?|??TABLE?ACCESS?FULL|?T1???|???531?|?93987?|???159???(2)|?00:00:02?| ?-------------------------------------------------------------------------- ?Predicate?Information?(identified?by?operation?id): ?--------------------------------------------------- ????1?-?filter("OBJECT_TYPE"='INDEX') ??Note ?----- ????-?dynamic?sampling?used?for?this?statement? 綜上所述：
1：可以對線上數據庫的組合索引做優化，對于傾斜字段做前導列的組合索引，可以使用非傾斜字段做前導列，或者建立相同的索引，前導列對調；
2：取消相應的函數索引
3：刪除不必要的組合索引，對經常在where子句中出現的字段建組合索引(例如查詢1中where子句出現A,B,C,D四個字段，查詢2中where子句出現A,B,C三個字段，且這個查詢語句經常出現，這種條件下，只需要對A,B,C,D字段建組合索引即可，無需建2個索引)
4：注意索引的熱點塊問題，前面3的場景在并發嚴重的情況下，有可能會導致出現熱點快，因而需要根據需求來適當調整
總結
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