ORACLE使用GV_$TEMP_SPACE_HEADER統計臨時表空使用狀況不許確的問題

之前寫了一篇ORACLE臨時表空間總結的文章， 裏面介紹了幾個查看臨時表空間使用狀況的腳本，其中一個腳本以下所示：

 

SELECT TU.TABLESPACE_NAME                                    AS "TABLESPACE_NAME",

       TT.TOTAL - TU.USED                                    AS "FREE(G)",

       TT.TOTAL                                              AS "TOTAL(G)",

       ROUND(NVL(TU.USED, 0) / TT.TOTAL * 100, 3)            AS "USED(%)",

       ROUND(NVL(TT.TOTAL - TU.USED, 0) * 100 / TT.TOTAL, 3) AS "FREE(%)"

FROM (SELECT TABLESPACE_NAME, 

              SUM(BYTES_USED) / 1024 / 1024 / 1024 USED

       FROM GV_$TEMP_SPACE_HEADER

       GROUP BY TABLESPACE_NAME) TU ,

     (SELECT TABLESPACE_NAME,

              SUM(BYTES) / 1024 / 1024 / 1024 AS TOTAL

       FROM DBA_TEMP_FILES

       GROUP BY TABLESPACE_NAME) TT

WHERE TU.TABLESPACE_NAME = TT.TABLESPACE_NAME;

 

其實這個查看錶空間的腳本是不許確的，有問題的（固然前面博客裏面所提到的腳本到如今也沒有改，之後也不打算修改了，就這樣放着吧）。你能夠對比下面幾個腳原本看看。

   

若是臨時表空間是dictionary managed temporary tablespace，可使用下面SQL：

SELECT (S.TOT_USED_BLOCKS/F.TOTAL_BLOCKS)*100 AS "PERCENT USED"

FROM

  (SELECT SUM(USED_BLOCKS) TOT_USED_BLOCKS

  FROM V$SORT_SEGMENT

  WHERE TABLESPACE_NAME='TEMPSCM2'

  ) S,

  (SELECT SUM(BLOCKS) TOTAL_BLOCKS

  FROM DBA_DATA_FILES

  WHERE TABLESPACE_NAME='TEMPSCM2'

  ) F;

 

若是臨時表空間是Locally Manageed Temporary Tablespace，使用下面SQL：

SQL> SELECT  T.TABLESPACE_NAME,

            ( U.TOT_USED_BLOCKS / T.TOTAL_BLOCKS ) * 100 AS "PERCENT USED" 

     FROM   (SELECT TABLESPACE_NAME,

                    SUM(USED_BLOCKS) TOT_USED_BLOCKS 

             FROM   V$SORT_SEGMENT 

             WHERE  TABLESPACE_NAME = &TABLESPACE_NAME

             GROUP BY TABLESPACE_NAME) U, 

            (SELECT TABLESPACE_NAME,

                    SUM(BLOCKS) TOTAL_BLOCKS 

             FROM   DBA_TEMP_FILES 

             WHERE  TABLESPACE_NAME = &TABLESPACE_NAME

             GROUP BY TABLESPACE_NAME) T;

 

固然你也可使用下面SQL來查看臨時表空間的使用狀況， 以下所示：

SELECT D.tablespace_name, 

               SPACE                                      "SUM_SPACE(M)", 

               blocks                                     "SUM_BLOCKS", 

               used_space                                 "USED_SPACE(M)", 

               Round(Nvl(used_space, 0) / SPACE * 100, 2) "USED_RATE(%)", 

               SPACE - used_space                         "FREE_SPACE(M)" 

        FROM   (SELECT tablespace_name, 

                       Round(SUM(bytes) / ( 1024 * 1024 ), 2) SPACE, 

                       SUM(blocks)                            BLOCKS 

                FROM   dba_temp_files 

                GROUP  BY tablespace_name) D, 

               (SELECT tablespace, 

                       Round(SUM(blocks * 8192) / ( 1024 * 1024 ), 2) USED_SPACE 

                FROM   v$sort_usage 

                GROUP  BY tablespace) F 

        WHERE  D.tablespace_name = F.tablespace(+)

          AND  D.tablespace_name='TEMPSCM2'

 

 

那麼爲何GV_$TEMP_SPACE_HEADER統計的數據不許確呢？ 這個是由於GV_$TEMP_SPACE_HEADER取數據不許確，官方解釋爲：

 

The views v$sort_usage or v$tempseg_usage ( and v$sort_segment) give the correct information regarding the allocation of sort segments.

We should always query these views to find out the actual temp usage. The view v$temp_space_header shows that these many blocks were touched in each temp file at some point when temp usage was at its highest,

in essence, it shows the number of initialized blocks for each tempfile, not the actual allocated blocks.

The views v$sort_usage/v$tempseg_usage show the actual sort extents allocated for each transaction from these initialized blocks. Also, v$temp_space_header is persistent across restarts. V$sort_segment and v$sort_usage are not.

 

 

第二段我翻譯以下：

視圖v$temp_space_header顯示的是每個temp文件在某一個時刻使用過的最大大小，從本質上說，它顯示的是每個tempfile的初始化大小，而不是實際分配的塊大小。

 

因此說從視圖v$temp_space_header獲取的數據其實並非實際使用的大小，它是不許確的。那麼確定有人會問，腳本里面不是訪問的GV_$TEMP_SPACE_HEADER視圖嗎? 跟這個視圖v$temp_space_header有關係嗎？ 答案是有關係，他們的數據來源是一致的，也就是說來自相同的內部表，以下所示：

 

通常來講，在GV$和V$以後， Oracle會創建GV_$和V_$視圖， 隨後爲這些視圖創建了公用同義詞。GV_$TEMP_SPACE_HEADER是一個視圖，以下所示

SQL> SELECT OWNER, OBJECT_NAME, OBJECT_TYPE FROM DBA_OBJECTS WHERE OBJECT_NAME ='GV_$TEMP_SPACE_HEADER';

OWNER                   OBJECT_NAME                         OBJECT_TYPE

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

SYS                     GV_$TEMP_SPACE_HEADER                VIEW

 

GV_$TEMP_SPACE_HEADER視圖的定義以下所示：

SELECT DBMS_METADATA.GET_DDL('VIEW', 'GV_$TEMP_SPACE_HEADER', 'SYS') FROM DUAL;

SELECT * FROM DBA_VIEWS WHERE VIEW_NAME='GV_$TEMP_SPACE_HEADER';

SELECT "INST_ID",

 "TABLESPACE_NAME",

 "FILE_ID",

 "BYTES_USED",

 "BLOCKS_USED",

 "BYTES_FREE",

 "BLOCKS_FREE",

 "RELATIVE_FNO"

ROM gv$temp_space_header

 

 

而gv$temp_space_header視圖的定義以下（固然若是查詢DBA_OBJECTS會發現它是一個同義詞，指向GV_$TEMP_SPACE_HEADER,這個後面介紹緣由)

SQL>  select view_definition from v$fixed_view_definition

  2  where view_name='GV$TEMP_SPACE_HEADER';

VIEW_DEFINITION

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

select /*+ ordered use_nl(hc) */ hc.inst_id, ts.name, hc.ktfthctfno, (hc.ktfthcs

z - hc.ktfthcfree)*ts.blocksize, (hc.ktfthcsz - hc.ktfthcfree), hc.ktfthcfree*ts

.blocksize, hc.ktfthcfree, hc.ktfthcfno from ts$ ts, x$ktfthc hc where ts.conten

ts$ = 1 and ts.bitmapped <> 0 and ts.online$ = 1 and ts.ts# = hc.ktfthctsn and h

c.ktfthccval = 0

SQL> 

 

 

v$temp_space_header它也是一個視圖（查詢DBA_OBJECTS發現其是一個同義詞，這個後面介紹），你會發現v$temp_space_header實際上是從視圖GV$TEMP_SPACE_HEADER過濾數據，以下所示：

SELECT OWNER, OBJECT_NAME, OBJECT_TYPE FROM DBA_OBJECTS WHERE OBJECT_NAME =upper('v$temp_space_header');

QL> select view_definition from v$fixed_view_definition

 2   where view_name=upper('v$temp_space_header');

IEW_DEFINITION

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

elect  TABLESPACE_NAME , FILE_ID , BYTES_USED , BLOCKS_USED , BYTES_FREE , BLOC

S_FREE , RELATIVE_FNO from GV$TEMP_SPACE_HEADER where inst_id = USERENV('Instan

e')

 

你在$ORACLE_HOME/rdbms/admin下的catspace.sql中，就會發現這樣的SQL，這就解釋了爲何gv$temp_space_header是視圖，又是同義詞的緣由。

create or replace view gv_$temp_space_header as select * from gv$temp_space_header;

create or replace public synonym gv$temp_space_header

   for gv_$temp_space_header;

grant select on gv_$temp_space_header to SELECT_CATALOG_ROLE;