查看執行計劃的方法

Explain Plan For SQL

不實際執行SQL語句，生成的計劃未必是真實執行的計劃

必須要有plan_table

SQLPLUS AUTOTRACE

除set autotrace traceonly explain外均實際執行SQL，但仍未必是真實計劃

必須要有plan_table

SQL TRACE

需要啟用10046戒者SQL_TRACE

一般用tkprof看的更清楚些，當然10046里本身也有執行計劃信息

V$SQL和V$SQL_PLAN

可以查詢到多個子游標的計劃信息了，但是看起來比較費勁

Enterprise Manager

可以圖形化顯示執行計劃，但并非所有環境有EM可用

其他第三方工具

注意 PL/SQL developer之類工具F5看到的執行計劃未必是真實的

推薦的方法 DBMS_XPLAN

select * from table(dbms_xplan….);

dbms_xplan.display()

數據來源是Plan Table

dbms_xplan.display_cursor

數據來源是Shared pool中的游標緩存

FUNCTION DISPLAY_CURSOR RETURNS DBMS_XPLAN_TYPE_TABLE

Argument Name Type In/Out Default?

------------------------------ ----------------------- ------ --------

SQL_ID VARCHAR2 IN DEFAULT

CURSOR_CHILD_NO NUMBER(38) IN DEFAULT

FORMAT VARCHAR2 IN DEFAULT

推薦的使用參數為：

select * from table(dbms_xplan.display_cursor('sqlId',null,'ADVANCED ALLSTATS LAST PEEKED_BINDS'));

如果sqlId為NULL，則顯示當前session的執行計劃。

select * from table(dbms_xplan.display_cursor(null,null,'ADVANCED ALLSTATS LAST PEEKED_BINDS'));

其中format的解釋如下：

IOSTATS: Assuming that basic plan statistics are

--- collected when SQL statements are executed (either by

--- using the gather_plan_statistics hint or by setting the

--- parameter statistics_level to ALL), this format will show

--- IO statistics for all (or only for the last as shown below)

--- executions of the cursor.

---

--- MEMSTATS: Assuming that PGA memory management is enabled (i.e

--- pga_aggregate_target parameter is set to a non 0 value),

--- this format allows to display memory management

--- statistics (e.g. execution mode of the operator, how

--- much memory was used, number of bytes spilled to

--- disk, ...). These statistics only apply to memory

--- intensive operations like hash-joins, sort or some bitmap

--- operators.

---

--- ROWSTATS: Assuming that basic plan statistics are

--- collected when SQL statements are executed (either by

--- using the gather_plan_statistics hint or by setting the

--- parameter statistics_level to ALL), this format will show

--- row count statistics for all (or only for the last as

--- shown below) executions of the cursor.

---

--- ALLSTATS: A shortcut for 'IOSTATS MEMSTATS ROWSTATS'

---

--- LAST: By default, plan statistics are shown for all executions of

--- the cursor. The keyword LAST can be specified to see only

--- the statistics for the last execution.

---

--- PEEKED_BINDS：顯示解析時使用的綁定變量。

dbms_xplan.display_awr

數據來源是AWR倉庫基表WRH$_SQL_PLAN

FUNCTION DISPLAY_AWR RETURNS DBMS_XPLAN_TYPE_TABLE

Argument Name Type In/Out Default?

------------------------------ ----------------------- ------ --------

SQL_ID VARCHAR2 IN

PLAN_HASH_VALUE NUMBER(38) IN DEFAULT

DB_ID NUMBER(38) IN DEFAULT

FORMAT VARCHAR2 IN DEFAULT

CON_ID NUMBER(38) IN DEFAULT

dbms_xplan.display_sqlset

數據來源是SQL Set視圖

以上內容主要整理自maclean的oracle執行計劃教學視頻和ppt：

www.askmaclean.com/archives/read-sql-execution-plan.html

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