[20120206]Cursor Invalidation與分析表.txt

在分析表的是否有一個引數no_invalidate：預設值是DBMS_STATS.AUTO_INVALIDATE.AUTO_INVALIDATE。

    10g中預設是AUTO_INVALIDATE，就是說分析表後，遊標不會馬上invalidate，已經存在的SQL的執行計劃不會受新的統計資訊影響。可以手工DDL
invalidate遊標。又或者等待隱藏引數_optimizer_invalidation_period(time window for invalidation of cursors of analyzed objects)秒後,
Oracle自動invalidate遊標並使SQL能夠讀取新的統計資訊產生新的執行計劃。

    如果想要dbms_stats分析立馬見效,需要使用no_invalidate=false option或者DBA自己手工invalidate遊標。

--說明一下，我個人感覺這個引數理解起來很煩，validate表示有效，no_invalidate反了2次,也是表示有效的意思。

dbms_stats收集統計資訊時候no_invalidate引數
用於是否與收集相關object的cursor失效，defalut(9i false, 10g dbms_stats.auto_invalidate(既null))
true：當收集完統計資訊後，收集物件的cursor不會失效（不會產生新的執行計劃，子游標）
false:當收集完統計資訊後，收集物件的cursor會立即失效（新的執行計劃，新的子游標）
no_invalidate=>DBMS_STATS.AUTO_INVALIDATE，分析表後，遊標不會馬上invalidate，已經存在的SQL的執行計劃不會受新的統計資訊影響。可以手工
DDL invalidate遊標。又或者等待隱藏引數_optimizer_invalidation_period(time window for invalidation of cursors of analyzed objects)秒後,
Oracle自動invalidate遊標並使SQL能夠讀取新的統計資訊產生新的執行計劃。


1.建立測試環境:
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

SQL> create table t as select rownum id , 'test' name from dual connect by level<=64;
SQL> exec dbms_stats.gather_table_stats(null,'t',no_invalidate => DBMS_STATS.AUTO_INVALIDATE);

SQL> select count(*) from t;
  COUNT(*)
----------
        64

--獲取sql_id

SQL> @dpc

PLAN_TABLE_OUTPUT

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

SQL_ID  cyzznbykb509s, child number 0

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

select count(*) from t

Plan hash value: 2966233522

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

| Id  | Operation          | Name | E-Rows | Cost (%CPU)|

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

|   0 | SELECT STATEMENT   |      |        |     3 (100)|

|   1 |  SORT AGGREGATE    |      |      1 |            |

|   2 |   TABLE ACCESS FULL| T    |     64 |     3   (0)|

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

sqlid='cyzznbykb509s'

2.測試1(no_invalidate => false):
SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';

SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          1           1          1             0


SQL> exec dbms_stats.gather_table_stats(null,'t',no_invalidate => false);
PL/SQL procedure successfully completed.

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          1           1          1             1
--分析後no_invalidate => false,v$sql 的INVALIDATIONS=1.游標失效。

SQL> select count(*) from t;
  COUNT(*)
----------
        64

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          1           1          2             1

3.測試2(no_invalidate => true):

SQL> exec dbms_stats.gather_table_stats(null,'t',no_invalidate => true);

PL/SQL procedure successfully completed.

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          1           1          2             1

--分析後no_invalidate => true,v$sql 的INVALIDATIONS=1（沒有變化與上次一樣）.說明游標沒有失效。

SQL> select count(*) from t;
  COUNT(*)
----------
        64

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          2           2          2             1

--再次執行查詢，發現PARSE_CALLS增加了1次，loads沒有變化。

4.測試3（no_invalidate => DBMS_STATS.AUTO_INVALIDATE):
預設隱藏引數_optimizer_invalidation_period設定的時間太長=18000（5個小時），我縮短一些。

SQL> alter system set "_optimizer_invalidation_period" = 300 scope=memory;
System altered.

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          2           2          2             1

--馬上執行，select count(*) from t;
SQL> exec dbms_stats.gather_table_stats(null,'t',no_invalidate => DBMS_STATS.AUTO_INVALIDATE);
PL/SQL procedure successfully completed.

SQL> select count(*) from t;
  COUNT(*)
----------
        64

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          3           3          2             1

--可以發現v$sql 的INVALIDATIONS=1（沒有變化與上次）.說明游標沒有失效。執行計劃以及使用原來的游標。
--等一段時間300秒，再測試：

SQL> host sleep 300

SQL> select count(*) from t;
  COUNT(*)
----------
        64

SQL> select sql_id,child_number,executions,parse_calls,loads,invalidations from v$sql where sql_id = 'cyzznbykb509s';
SQL_ID        CHILD_NUMBER EXECUTIONS PARSE_CALLS      LOADS INVALIDATIONS
------------- ------------ ---------- ----------- ---------- -------------
cyzznbykb509s            0          3           3          2             1
cyzznbykb509s            1          1           1          1             0


--可以發現原來的游標無效，生成新的子游標。看看為什麼不能共享？

SQL> @share cyzznbykb509s
old  15:           and q.sql_id like ''&1''',
new  15:           and q.sql_id like ''cyzznbykb509s''',
SQL_TEXT                       = select count(*) from t
SQL_ID                         = cyzznbykb509s
ADDRESS                        = 000000009353C428
CHILD_ADDRESS                  = 0000000093623B88
CHILD_NUMBER                   = 0
--------------------------------------------------
SQL_TEXT                       = select count(*) from t
SQL_ID                         = cyzznbykb509s
ADDRESS                        = 000000009353C428
CHILD_ADDRESS                  = 000000009362C7E0
CHILD_NUMBER                   = 1
ROLL_INVALID_MISMATCH          = Y
--------------------------------------------------
PL/SQL procedure successfully completed.

--原來的游標無效，是由於ROLL_INVALID_MISMATCH。最後修改隱含引數回來。
SQL> alter system set "_optimizer_invalidation_period" = 18000 scope=memory;
System altered.

總結：
    預設分析DBMS_STATS.AUTO_INVALIDATE，如果處理不好，一些效能問題會延遲出現，在最佳化時注意。
    
share指令碼如下：
SET  serveroutput on size 100000;

DECLARE
   c           NUMBER;
   col_cnt     NUMBER;
   col_rec     DBMS_SQL.desc_tab;
   col_value   VARCHAR2 (4000);
   ret_val     NUMBER;
BEGIN
   c := DBMS_SQL.open_cursor;
   DBMS_SQL.parse
      (c,
       'select q.sql_text, s.*
      from v$sql_shared_cursor s, v$sql q
      where s.sql_id = q.sql_id
          and s.child_number = q.child_number
          and q.sql_id like ''&1''',
       DBMS_SQL.native
      );
   DBMS_SQL.describe_columns (c, col_cnt, col_rec);

FOR idx IN 1 .. col_cnt
   LOOP
      DBMS_SQL.define_column (c, idx, col_value, 4000);
   END LOOP;

   ret_val := DBMS_SQL.EXECUTE (c);

   WHILE (DBMS_SQL.fetch_rows (c) > 0)
   LOOP
      FOR idx IN 1 .. col_cnt
      LOOP
         DBMS_SQL.COLUMN_VALUE (c, idx, col_value);

         IF col_rec (idx).col_name IN
               ('SQL_ID', 'ADDRESS', 'CHILD_ADDRESS', 'CHILD_NUMBER',
                'SQL_TEXT')
         THEN
            DBMS_OUTPUT.put_line (   RPAD (col_rec (idx).col_name, 30)
                                  || ' = '
                                  || col_value
                                 );
         ELSIF col_value = 'Y'
         THEN
            DBMS_OUTPUT.put_line (   RPAD (col_rec (idx).col_name, 30)
                                  || ' = '
                                  || col_value
                                 );
         END IF;
      END LOOP;

      DBMS_OUTPUT.put_line
                         ('--------------------------------------------------');
   END LOOP;

   DBMS_SQL.close_cursor (c);
END;
/

SET serveroutput off;