檢視sql 執行計劃的歷史變更

oracle 10G 以後可以透過下面的三個檢視查詢到sql執行計劃的歷史資訊：
DBA_HIST_SQL_PLAN
DBA_HIST_SQLSTAT
DBA_HIST_SNAPSHOT

檢視語句的歷史執行資訊，是否發生變化，何時發生了變化。如果發生了變化,找出以前的執行計劃,與當前的執行計劃進行對比,有什麼不同。
使用如下sql 可以發現某個sql的執行計劃什麼時候發生了變化！
select distinct SQL_ID,
                PLAN_HASH_VALUE,
                to_char(TIMESTAMP, 'yyyymmdd hh24:mi:ss') TIMESTAMP
from dba_hist_sql_plan
where SQL_ID = '68wnxdjxwwn2h'
order by TIMESTAMP;

SQL_ID        PLAN_HASH_VALUE TIMESTAMP
------------- --------------- -----------------
68wnxdjxwwn2h       235510920 20111020 21:25:23
68wnxdjxwwn2h      1542630049 20120612 11:57:23
68wnxdjxwwn2h      2754593971 20120612 12:43:34

檢視出來執行計劃的變化之後可以使用如下sql檢視發生了那些變化！
col options for a15
col operation for a20
col object_name for a20
select plan_hash_value,
       id,
       operation,
       options,
       object_name,
       depth,
       cost,
       to_char(TIMESTAMP, 'yyyymmdd hh24:mi:ss')
from DBA_HIST_SQL_PLAN
where sql_id = '68wnxdjxwwn2h'
   and plan_hash_value in (1542630049, 2754593971, 2620382595)
order by TIMESTAMP,ID;

PLAN_HASH_VALUE         ID OPERATION             OPTIONS         OBJECT_NAME                 COST TO_CHAR(TIMESTAMP
--------------- ---------- --------------------- --------------- --------------------- ---------- -----------------
      235510920          0 SELECT STATEMENT                                                    39 20111020 21:25:23
      235510920          1 NESTED LOOPS                                                           20111020 21:25:23
      235510920          2 NESTED LOOPS                                                        39 20111020 21:25:23
      235510920          3 VIEW                                                                11 20111020 21:25:23
      235510920          4 WINDOW                SORT PUSHED RANK                               11 20111020 21:25:23
      235510920          5 TABLE ACCESS          FULL            C_ETL_DATA_VALIDITY           10 20111020 21:25:23
      235510920          6 PARTITION LIST        ITERATOR                                       2 20111020 21:25:23
      235510920          7 INDEX                 RANGE SCAN      IDX_C_MEM_XXXXXXXX_ID          2 20111020 21:25:23
      235510920          8 TABLE ACCESS          BY LOCAL INDEX C_MEM_XXXXXXXX_FATDT0          4 20111020 21:25:23
                                                 ROWID
     1542630049          0 SELECT STATEMENT                                                  7854 20120612 11:57:23
     1542630049          1 NESTED LOOPS                                                      7854 20120612 11:57:23
     1542630049          2 VIEW                                                                28 20120612 11:57:23
     1542630049          3 WINDOW                SORT PUSHED RANK                              28 20120612 11:57:23
     1542630049          4 TABLE ACCESS          FULL            C_ETL_DATA_VALIDITY           27 20120612 11:57:23
     1542630049          5 PARTITION LIST        ITERATOR                                    7826 20120612 11:57:23
     1542630049          6 TABLE ACCESS          FULL            C_MEM_XXXXXXXX_FATDT0       7826 20120612 11:57:23
     2754593971          0 SELECT STATEMENT                                                    43 20120612 12:43:34
     2754593971          1 PX COORDINATOR                                                         20120612 12:43:34
     2754593971          2 PX SEND               QC (RANDOM)     :TQ10001                         20120612 12:43:34
     2754593971          3 NESTED LOOPS                                                           20120612 12:43:34
     2754593971          4 NESTED LOOPS                                                        43 20120612 12:43:34
     2754593971          5 BUFFER                SORT                                             20120612 12:43:34
     2754593971          6 PX RECEIVE                                                             20120612 12:43:34
     2754593971          7 PX SEND               BROADCAST       :TQ10000                         20120612 12:43:34
     2754593971          8 VIEW                                                                28 20120612 12:43:34
     2754593971          9 WINDOW                SORT PUSHED RANK                              28 20120612 12:43:34
     2754593971         10 TABLE ACCESS          FULL            C_ETL_DATA_VALIDITY           27 20120612 12:43:34
     2754593971         11 PX PARTITION LIST     ITERATOR                                       2 20120612 12:43:34
     2754593971         12 INDEX                 RANGE SCAN      IDX_C_MEM_XXXXXXXX_ID          2 20120612 12:43:34
     2754593971         13 TABLE ACCESS          BY LOCAL INDEX C_MEM_XXXXXXXX_FATDT0         15 20120612 12:43:34
                                                 ROWID
     2620382595          0 SELECT STATEMENT                                                     5 20120612 18:27:37
     2620382595          1 TABLE ACCESS          BY INDEX ROWID C_MEM_XXXXXXXX_BAKUP           5 20120612 18:27:37
     2620382595          2 INDEX                 RANGE SCAN      IDX_C_MEM_XXXXXXXX_BA          3 20120612 18:27:37
                                                                 KUP_ID
33 rows selected.

從上面的結果中可以看出執行計劃在11:57 時出現改變 C_MEM_XXXXXXXX_FATDT0有之前的index range scan 變為了full table scan！

檢視sql 執行計劃的歷史變更

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