簡單對比檢視執行計劃的兩種方法EXPLAIN PLAN 和 AUTOTRACE
阿新 • • 發佈：2019-02-13
EXPLAIN PLAN 和 AUTOTRACE 都可以檢視執行計劃。 值得一提的是：前者只是優化器通過讀取資料字典的統計資訊做出'最佳'訪問路徑判斷，並沒有真正去執行語句；後者是實際去執行了SQL語句，同時把訪問記錄數、執行計劃、統計資訊等打印出來。
下面粘出實驗結果加以說明，注意對比兩者的耗時：
<p>SQL> CONNECT /AS SYSDBA Connected.</p><p>SQL> SET LINESIZE 300; SQL> SET TIMING ON; SQL> SET PAGESIZE; SQL> EXPLAIN PLAN FOR SELECT COUNT(*) FROM DBA_OBJECTS , DBA_OBJECTS;</p><p>Explained.</p><p>Elapsed: 00:00:00.03 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<僅消耗0.03秒 SQL> SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY); Plan hash value: 2343274122</p><p>------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 7187K (5)| 23:57:25 | | 1 | SORT AGGREGATE | | 1 | | | | | 2 | MERGE JOIN CARTESIAN | | 2325M| | 7187K (5)| 23:57:25 | | 3 | VIEW | DBA_OBJECTS | 48221 | | 149 (5)| 00:00:02 | | 4 | UNION-ALL | | | | | | |* 5 | FILTER | | | | | | |* 6 | HASH JOIN | | 51192 | 4099K| 148 (5)| 00:00:02 | | 7 | TABLE ACCESS FULL | USER$ | 59 | 177 | 2 (0)| 00:00:01 | |* 8 | TABLE ACCESS FULL | OBJ$ | 51192 | 3949K| 145 (5)| 00:00:02 | |* 9 | TABLE ACCESS BY INDEX ROWID | IND$ | 1 | 8 | 2 (0)| 00:00:01 | |* 10 | INDEX UNIQUE SCAN | I_IND1 | 1 | | 1 (0)| 00:00:01 | | 11 | NESTED LOOPS | | 1 | 16 | 1 (0)| 00:00:01 | | 12 | INDEX FULL SCAN | I_LINK1 | 1 | 13 | 0 (0)| 00:00:01 | | 13 | TABLE ACCESS CLUSTER | USER$ | 1 | 3 | 1 (0)| 00:00:01 | |* 14 | INDEX UNIQUE SCAN | I_USER# | 1 | | 0 (0)| 00:00:01 | | 15 | BUFFER SORT | | 48221 | | 7187K (5)| 23:57:25 | | 16 | VIEW | DBA_OBJECTS | 48221 | | 149 (5)| 00:00:02 | | 17 | UNION-ALL | | | | | | |* 18 | FILTER | | | | | | |* 19 | HASH JOIN | | 51192 | 4099K| 148 (5)| 00:00:02 | | 20 | TABLE ACCESS FULL | USER$ | 59 | 177 | 2 (0)| 00:00:01 | |* 21 | TABLE ACCESS FULL | OBJ$ | 51192 | 3949K| 145 (5)| 00:00:02 | |* 22 | TABLE ACCESS BY INDEX ROWID| IND$ | 1 | 8 | 2 (0)| 00:00:01 | |* 23 | INDEX UNIQUE SCAN | I_IND1 | 1 | | 1 (0)| 00:00:01 | | 24 | NESTED LOOPS | | 1 | 16 | 1 (0)| 00:00:01 | | 25 | INDEX FULL SCAN | I_LINK1 | 1 | 13 | 0 (0)| 00:00:01 | | 26 | TABLE ACCESS CLUSTER | USER$ | 1 | 3 | 1 (0)| 00:00:01 | |* 27 | INDEX UNIQUE SCAN | I_USER# | 1 | | 0 (0)| 00:00:01 | -------------------------------------------------------------------------------------------------</p><p>Predicate Information (identified by operation id): ---------------------------------------------------</p><p> 5 - filter("O"."TYPE#"<>1 AND "O"."TYPE#"<>10 OR "O"."TYPE#"=1 AND (SELECT 1 FROM "SYS"."IND$" "I" WHERE "I"."OBJ#"=:B1 AND ("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9))=1) 6 - access("O"."OWNER#"="U"."USER#") 8 - filter(BITAND("O"."FLAGS",128)=0 AND "O"."NAME"<>'_NEXT_OBJECT' AND "O"."NAME"<>'_default_auditing_options_' AND "O"."LINKNAME" IS NULL) 9 - filter("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9) 10 - access("I"."OBJ#"=:B1) 14 - access("L"."OWNER#"="U"."USER#") 18 - filter("O"."TYPE#"<>1 AND "O"."TYPE#"<>10 OR "O"."TYPE#"=1 AND (SELECT 1 FROM "SYS"."IND$" "I" WHERE "I"."OBJ#"=:B1 AND ("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9))=1) 19 - access("O"."OWNER#"="U"."USER#") 21 - filter(BITAND("O"."FLAGS",128)=0 AND "O"."NAME"<>'_NEXT_OBJECT' AND "O"."NAME"<>'_default_auditing_options_' AND "O"."LINKNAME" IS NULL) 22 - filter("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9) 23 - access("I"."OBJ#"=:B1) 27 - access("L"."OWNER#"="U"."USER#")</p><p>58 rows selected.</p><p>Elapsed: 00:00:00.04</p>
<p>SQL> SET AUTOTRACE; Usage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]] SQL> SET AUTOTRACE ON; SQL> SELECT COUNT(*) FROM DBA_OBJECTS , DBA_OBJECTS; 2508707569 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<count()</p><p>Elapsed: 00:01:41.97 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<消耗1分41.97秒</p><p>Execution Plan ---------------------------------------------------------- Plan hash value: 2343274122</p><p>------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 7187K (5)| 23:57:25 | | 1 | SORT AGGREGATE | | 1 | | | | | 2 | MERGE JOIN CARTESIAN | | 2325M| | 7187K (5)| 23:57:25 | | 3 | VIEW | DBA_OBJECTS | 48221 | | 149 (5)| 00:00:02 | | 4 | UNION-ALL | | | | | | |* 5 | FILTER | | | | | | |* 6 | HASH JOIN | | 51192 | 4099K| 148 (5)| 00:00:02 | | 7 | TABLE ACCESS FULL | USER$ | 59 | 177 | 2 (0)| 00:00:01 | |* 8 | TABLE ACCESS FULL | OBJ$ | 51192 | 3949K| 145 (5)| 00:00:02 | |* 9 | TABLE ACCESS BY INDEX ROWID | IND$ | 1 | 8 | 2 (0)| 00:00:01 | |* 10 | INDEX UNIQUE SCAN | I_IND1 | 1 | | 1 (0)| 00:00:01 | | 11 | NESTED LOOPS | | 1 | 16 | 1 (0)| 00:00:01 | | 12 | INDEX FULL SCAN | I_LINK1 | 1 | 13 | 0 (0)| 00:00:01 | | 13 | TABLE ACCESS CLUSTER | USER$ | 1 | 3 | 1 (0)| 00:00:01 | |* 14 | INDEX UNIQUE SCAN | I_USER# | 1 | | 0 (0)| 00:00:01 | | 15 | BUFFER SORT | | 48221 | | 7187K (5)| 23:57:25 | | 16 | VIEW | DBA_OBJECTS | 48221 | | 149 (5)| 00:00:02 | | 17 | UNION-ALL | | | | | | |* 18 | FILTER | | | | | | |* 19 | HASH JOIN | | 51192 | 4099K| 148 (5)| 00:00:02 | | 20 | TABLE ACCESS FULL | USER$ | 59 | 177 | 2 (0)| 00:00:01 | |* 21 | TABLE ACCESS FULL | OBJ$ | 51192 | 3949K| 145 (5)| 00:00:02 | |* 22 | TABLE ACCESS BY INDEX ROWID| IND$ | 1 | 8 | 2 (0)| 00:00:01 | |* 23 | INDEX UNIQUE SCAN | I_IND1 | 1 | | 1 (0)| 00:00:01 | | 24 | NESTED LOOPS | | 1 | 16 | 1 (0)| 00:00:01 | | 25 | INDEX FULL SCAN | I_LINK1 | 1 | 13 | 0 (0)| 00:00:01 | | 26 | TABLE ACCESS CLUSTER | USER$ | 1 | 3 | 1 (0)| 00:00:01 | |* 27 | INDEX UNIQUE SCAN | I_USER# | 1 | | 0 (0)| 00:00:01 | -------------------------------------------------------------------------------------------------</p><p>Predicate Information (identified by operation id): ---------------------------------------------------</p><p> 5 - filter("O"."TYPE#"<>1 AND "O"."TYPE#"<>10 OR "O"."TYPE#"=1 AND (SELECT 1 FROM "SYS"."IND$" "I" WHERE "I"."OBJ#"=:B1 AND ("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9))=1) 6 - access("O"."OWNER#"="U"."USER#") 8 - filter(BITAND("O"."FLAGS",128)=0 AND "O"."NAME"<>'_NEXT_OBJECT' AND "O"."NAME"<>'_default_auditing_options_' AND "O"."LINKNAME" IS NULL) 9 - filter("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9) 10 - access("I"."OBJ#"=:B1) 14 - access("L"."OWNER#"="U"."USER#") 18 - filter("O"."TYPE#"<>1 AND "O"."TYPE#"<>10 OR "O"."TYPE#"=1 AND (SELECT 1 FROM "SYS"."IND$" "I" WHERE "I"."OBJ#"=:B1 AND ("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9))=1) 19 - access("O"."OWNER#"="U"."USER#") 21 - filter(BITAND("O"."FLAGS",128)=0 AND "O"."NAME"<>'_NEXT_OBJECT' AND "O"."NAME"<>'_default_auditing_options_' AND "O"."LINKNAME" IS NULL) 22 - filter("I"."TYPE#"=1 OR "I"."TYPE#"=2 OR "I"."TYPE#"=3 OR "I"."TYPE#"=4 OR "I"."TYPE#"=6 OR "I"."TYPE#"=7 OR "I"."TYPE#"=9) 23 - access("I"."OBJ#"=:B1) 27 - access("L"."OWNER#"="U"."USER#")</p><p> Statistics ---------------------------------------------------------- 15 recursive calls 0 db block gets 10208 consistent gets 0 physical reads 0 redo size 519 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 1 sorts (memory) 0 sorts (disk) 1 rows processed <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<返回1條結果集</p>
因此，EXPLAIN PLAN時常不能反應真實的執行計劃，尤其是在繫結變數的應用中。PLSQL/DEVELOPER的F5能快速檢視執行計劃，其實就是EXPLAIN PLAN的方法。
如果想知道SQL語句的真實執行計劃，可能通過以下幾種方法：
o SET AUOTRACE
o 10046
o DBMS_XPLAN.DISPLAY_COURSOR 或 DBMS_XPLAN.DISPLAY_AWR
o 查詢V$SQL_PLAN