關於free lists

segment header
 If the contention is on the segment header, then this is most likely free
list contention.
如果壓力存在於segment的頭部，那麼這最可能是free list壓力。

Automatic segment-space management in locally managed tablespaces eliminates the
need to specify the PCTUSED, FREELISTS, and FREELIST GROUPS parameters.

在本地管理資料表空間中的自動段管理機製革除了使用pctused 、FREELISTS,以及freelists  groups的需要。

If possible, switch from manual space management to automatic segment-space
management (ASSM).
如果可能，從手動空間管理切換到自動段空間管理(ASSM)

The following information is relevant if you are unable to use automatic
segment-space management (for example, because the tablespace uses dictionary
space management).

下面的資訊是由價值的，如果你不能使用自動段管理來管理資料表空間。（比如說，資料表空間
使用字典資料表空間管理員模式）

 

A free list is a list of free data blocks that usually includes blocks existing in a number
of different extents within the segment.

一個空白列表，是這樣一個空閑資料區塊的列表，它一般包含在某一個segment裡的
一系列extents中。

Free lists are composed of blocks in which free
space has not yet reached PCTFREE or used space has shrunk below PCTUSED.
Specify the number of process free lists with the FREELISTS parameter. The default
value of FREELISTS is one. The maximum value depends on the data block size.

空閑列表包含的資料區塊，裡面的空閑空間還沒達到PCTFREE ，或者使用的 空間已經減縮到
PCTUSED。使用FREELISTS參數 來指定一系列進程空閑列表。預設的FREELISTS 參數
數值是1。最大的數值要依據資料區塊的大小而定.

To find the current setting for free lists for that segment, run the following:
SELECT SEGMENT_NAME, FREELISTS
FROM DBA_SEGMENTS
WHERE SEGMENT_NAME = segment name
AND SEGMENT_TYPE = segment type;

查看某個segment裡面的當前free lists設定，可以用下面的指令碼，
SELECT SEGMENT_NAME, FREELISTS
FROM DBA_SEGMENTS
WHERE SEGMENT_NAME = segment name
AND SEGMENT_TYPE = segment type;

 

Set free lists, or increase the number of free lists. If adding more free lists does not
alleviate the problem, then use free list groups (even in single instance this can make a
difference). If using Oracle Real Application Clusters, then ensure that each instance
has its own free list group(s).

設定free lists，或者增加free lists的個數。如果增加更多的free lists 不能減輕問題，
那就使用free list 組（即使在單一實例情況下也能有好的效果。如果使用oracle
RAC,那麼請確認每個執行個體有自己的free lists 組。

 

See Also: Oracle Database Concepts for information on automatic
segment-space management, free lists, PCTFREE, and PCTUSED