Oracle Temp 臨時表空間

一.  Temporary Tablespacs 說明

            A temporary tablespace contains transient data that persists only for the duration of a session. No permanent schema objects can reside in a temporary tablespace. The database stores temporary tablespace data in temp files.

            Temporary tablespaces can improve the concurrency of multiple sort operations that do not fit in memory. These tablespaces also improve the efficiency of space management operations during sorts.

            When the SYSTEM tablespace is locally managed, a default temporary tablespace is included in the database by default during database creation. A locally managed SYSTEM tablespace cannot serve as default temporary storage.

            -- 本地管理的system 表空間，不能作為預設的臨時表空間。

 

            You cannot make a default temporary tablespace permanent.

            You can specify a user-named default temporary tablespace when you create a database by using the DEFAULT TEMPORARY TABLESPACE extension to the CREATE DATABASE statement. If SYSTEM is dictionary managed, and if a default temporary tablespace is not defined at database creation, then SYSTEM is the default temporary storage. However, the database writes a warning in the alert logsaying that a default temporary tablespace is recommended.

            -- 當SYSTEM 表空間是資料字典管理時，並且沒有定義預設的臨時表空間，那麼SYSTEM 表空間會作為預設的temporary storage。

 

            關於表空間的兩種型別： locally managed 和 dictionary managed的區別，參考我的Blog：

            Oracle 自動段空間管理(ASSM:auto segment space management)

            http://space.itpub.net/15880878/viewspace-720058

 

 

            A temporary tablespace contains schema objects only for the duration of a session. Locally managed temporary tablespaces have temporary files (temp files), which are special files designed to store data in hash, sort, and other operations. Temp files also store result set data when insufficient space exists in memory.

 

Temp files are similar to permanent data files, with the following exceptions:

（1）Permanent database objects such as tables are never stored in temp files.

（2）Temp files are always set to NOLOGGING mode, which means that they never have redo generated for them. Media recovery does not recognize temp files.

（3）You cannot make a temp file read-only.

（4）You cannot create a temp file with the ALTER DATABASE statement.

（5）When you create or resize temp files, they are not always guaranteed allocation of disk space for the file size specified. On file systems such as Linux and UNIX, temp files are created as sparse files. In this case, disk blocks are allocated not at file creation or resizing, but as the blocks are accessed for the first time.

Caution:

            Sparse files enable fast temp file creation and resizing; however, the disk could run out of space later when the temp files are accessed.

（6）Temp file information is shown in the data dictionary view DBA_TEMP_FILES and the dynamic performance view V$TEMPFILE, but not in DBA_DATA_FILES or the V$DATAFILE view.

 

            臨時表空間主要用途是在資料庫進行排序運算、管理索引、訪問檢視等操作時提供臨時的運算空間，當運算完成之後系統會自動清理。當oracle裡需要用到sort的時候，PGA中sort_area_size大小不夠時，將會把資料放入臨時表空間裡進行排序，同時如果有異常情況的話，也會被放入臨時表空間,正常來說，在完成Select語句、create index等一些使用TEMP表空間的排序操作後，Oracle是會自動釋放掉臨時段的。注意這裡的釋放，僅僅是將這些空間標記為空閒，並可重用，真正佔用的磁碟空間並沒有釋放。所以Temp表空間可能會越來越大。

 

            排序是很耗資源的，Temp表空間滿了,關鍵是優化你的語句，儘量使排序減少才是上策.

 

 

二.  Temp 表空間的操作

           

            You cannot use the ALTER TABLESPACE statement, with the TEMPORARY keyword, to change a locally managed permanent tablespace into a locally managed temporary tablespace. You must use the CREATE TEMPORARY TABLESPACE statement to create a locally managed temporary tablespace.

            You can use ALTER TABLESPACE to add a tempfile, take a tempfile offline, or bring a tempfile online, as illustrated in the following examples:

 

ALTER TABLESPACE lmtemp

   ADD TEMPFILE '/u02/oracle/data/lmtemp02.dbf' SIZE 18M REUSE;

 

SQL>ALTER TABLESPACE lmtemp TEMPFILE OFFLINE;

SQL>ALTER TABLESPACE lmtemp TEMPFILE ONLINE;

 

Note:

            You cannot take a temporary tablespace offline. Instead, you take its tempfile offline. The view V$TEMPFILE displays online status for a tempfile.

            -- 不可以將Temp 表空間offline，但是可以將tempfile offline。V$TEMPFILE 顯示了tempfile 的狀態。

 

The ALTER DATABASE statement can be used to alter tempfiles.

The following statements take offline and bring online tempfiles. They behave identically to the last two ALTER TABLESPACE statements in the previous example.

 

SQL>ALTER DATABASE TEMPFILE '/u02/oracle/data/lmtemp02.dbf' OFFLINE;

SQL>ALTER DATABASE TEMPFILE '/u02/oracle/data/lmtemp02.dbf' ONLINE;

 

The following statement resizes a tempfile: -- resize 表空間

SQL>ALTER DATABASE TEMPFILE '/u02/oracle/data/lmtemp02.dbf' RESIZE 18M;

 

The following statement drops a tempfile and deletes its operating system file:

SQL>ALTER DATABASE TEMPFILE '/u02/oracle/data/lmtemp02.dbf' DROP

    INCLUDING DATAFILES;

-- drop tempfile 和它的物理檔案。

 

            The tablespace to which this tempfile belonged remains. A message is written to the alert log for the tempfile that was deleted. If an operating system error prevents the deletion of the file, the statement still succeeds, but a message describing the error is written to the alert log.

            -- 當我們把temp 表空間的資料檔案檔案刪除之後，表空間的資訊還會存在，但是在alert log裡會有錯誤資訊。

 

            It is also possible to use the ALTER DATABASE statement to enable or disable the automatic extension of an existing tempfile, and to rename a tempfile. See Oracle Database SQL Language Reference for the required syntax.

 

Note:

            To rename a tempfile, you take the tempfile offline, use operating system commands to rename or relocate the tempfile, and then use the ALTER DATABASE RENAME FILE command to update the database controlfiles.

 

tempfile 資料檔案重新命名的步驟：

            （1）將tempfile offline       

            （2）在作業系統上重新命名tempfile

            （3）使用alter database rename file 更新控制檔案。

 

三. 臨時表空間滿時的處理方法

 

3.1 新增資料檔案

            如果Temporary tablespace還不大，那麼我們可以增加一些資料檔案。SQL 語句如下：

 

SQL>ALTER TABLESPACE TEMP ADD TEMPFILE 'D:/ORADATA/NEWCCS/TEMP02.DBF' SIZE 100M AUTOEXTEND OFF;

 

            一般來說，Temp tablespace 和 Undo Tablespace 是不建議設定為自增長，設定自增長可能會把磁碟給撐滿。

 

3.2 修改資料檔案大小

            可以將原來的資料檔案改大一點，如：

SQL>ALTER DATABASE TEMPFILE 'D:/ ORADATA/NEWCCS/TEMP02.DBF'

RESIZE 100M;

 

四. Temp 表空間過大的處理方法

            Temp 表空間過大，會佔用很多的磁碟空間，這時候，我們可以用一下2中方法來縮小temp 表空間的大小。

 

4.1  替換Temp 表空間

 

4.1.1  檢視目前Temp 表空間的資訊

SQL> select name from v$tempfile;

 

NAME

———————————————————————

D:/ORACLE/ORADATA/TEST/TEMP01.DBF

 

SQL> select username,temporary_tablespace from dba_users;

USERNAME            TEMPORARY_TABLESPACE

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

MGMT_VIEW                  TEMP

SYS                           TEMP

SYSTEM                       TEMP

DBSNMP                       TEMP

SYSMAN                       TEMP

 

            關於使用者這塊是要特別注意的，如果我們將預設的Temp 表空間指向其他的名稱，那麼這些使用者的資訊就會失效，所以，我們特換時，要麼建立一個臨時的Temp 表空間中轉一下，這樣切換之後，我們的temp表空間名稱不變，要麼改變名稱，同時更新相關使用者的default temp 表空間。

 

這裡用中轉的方法來測試。

 

4.1.2 建立中轉臨時表空間

 

            UNIFORM. specifies that the tablespace is managed with uniform. extents of SIZE bytes.The default SIZE is 1 megabyte. All extents of temporary tablespaces are of uniform. size, so this keyword is optional for a temporary tablespace. However, you must specify UNIFORM. in order to specify SIZE. You cannot specify UNIFORM. for an undo tablespace.

            -- Temp 表空間必須是uniform 的，undo 必須是autoallocate的。預設情況下uniform 是1M。

 

            If you do not specify AUTOALLOCATE or UNIFORM, then the default is UNIFORM. for temporary tablespaces and AUTOALLOCATE for all other types of tablespaces.

 

 

建立SQL 如下：

            SQL>CREATE TEMPORARY TABLESPACE TEMP2 TEMPFILE

  'D:/APP/ADMINISTRATOR/ORADATA/NEWCCS/TEMP03.DBF' SIZE 10M AUTOEXTEND OFF;

EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M;

 

上面是預設情況，等於一下SQL:

SQL>CREATE TEMPORARY TABLESPACE TEMP2 TEMPFILE

  'D:/APP/ADMINISTRATOR/ORADATA/NEWCCS/TEMP03.DBF' SIZE 10M AUTOEXTEND OFF

EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M;

 

4.1.3 修改Temp2為預設臨時表空間

SQL>alter database default temporary tablespace temp2;

 

4.1.4. 刪除原來臨時表空間

SQL>drop tablespace temp including contents and datafiles;

 

4.1.5.  重新建立臨時表空間

SQL>CREATE TEMPORARY TABLESPACE TEMP TEMPFILE

  'D:/APP/ADMINISTRATOR/ORADATA/NEWCCS/TEMP03.DBF' SIZE 10M AUTOEXTEND OFF;

EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M;

 

4.1.6. 重置預設臨時表空間為新建的temp表空間

SQL>alter database default temporary tablespace temp;

 

4.1.7. 刪除中轉用臨時表空間

SQL>drop tablespace temp2 including contents and datafiles;

 

4.1.8 如果有必要，重新指定使用者表空間為重建的臨時表空間

SQL>alter user dave temporary tablespace temp; 

 

4.2  Shrinking a Locally Managed Temporary Tablespace

            Large sort operations performed by the database may result in a temporary tablespace growing and occupying a considerable amount of disk space. After the sort operation completes, the extra space is not released; it is just marked as free and available for reuse.

            -- 當排序操作完成， 佔用的空間並沒有釋放，僅僅是將它標記為空閒，並可重用。

            Therefore, a single large sort operation might result in a large amount of allocated temporary space that remains unused after the sort operation is complete. For this reason, the database enables you to shrink locally managed temporary tablespaces and release unused space.

            --可以使用shrink 來釋放沒有使用的空間。

 

            （1）You use the SHRINK SPACE clause of the ALTER TABLESPACE statement to shrink a temporary tablespace, or （2）the SHRINK TEMPFILE clause of the ALTER TABLESPACE statement to shrink a specific tempfile of a temporary tablespace. Shrinking frees as much space as possible while maintaining the other attributes of the tablespace or tempfile. The optional KEEP clause defines a minimum size for the tablespace or tempfile.

 

            Shrinking is an online operation, which means that user sessions can continue to allocate sort extents if needed, and already-running queries are not affected.

            -- shrink 是一個online 的操作，不影響其他的查詢。

 

示例一：

            The following example shrinks the locally managed temporary tablespace lmtmp1 to a size of 20M.

            SQL>ALTER TABLESPACE lmtemp1 SHRINK SPACE KEEP 20M;

 

示例二：

            The following example shrinks the tempfile lmtemp02.dbf of the locally managed temporary tablespace lmtmp2. Because the KEEP clause is omitted, the database attempts to shrink the tempfile to the minimum possible size.

            SQL>ALTER TABLESPACE lmtemp2 SHRINK TEMPFILE '/u02/oracle/data/lmtemp02.dbf';

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