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LRU List [message #267004] Wed, 12 September 2007 04:22 Go to next message
Messages: 261
Registered: January 2006
Senior Member

Given below is the Oracle saying Oracle Database buffer management,

The buffers in the cache are organized in two lists: the write list and the least recently used (LRU) list. The write list holds dirty buffers, which contain data that has been modified but has not yet been written to disk. The LRU list holds free buffers, pinned buffers, and dirty buffers that have not yet been moved to the write list. Free buffers do not contain any useful data and are available for use. Pinned buffers are currently being accessed.

If the user process finds a dirty buffer as it searches the LRU list, it moves that buffer to the write list and continues to search. When the process finds a free buffer, it reads the data block from disk into the buffer and moves the buffer to the MRU end of the LRU list.

If an Oracle user process searches the threshold limit of buffers without finding a free buffer, the process stops searching the LRU list and signals the DBW0 background process to write some of the dirty buffers to disk.

I have some doubts based on this,please clear it,

1) Where the threshold limit for searching free buffers is set? How can i get value for this threshold limit?
2) Is Write List nothing but MRU List?
3) How long the pinned block will be in cache whether till the transaction completion or session completion?


[Updated on: Wed, 12 September 2007 04:49] by Moderator

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Re: LRU List [message #267019 is a reply to message #267004] Wed, 12 September 2007 04:58 Go to previous message
Michel Cadot
Messages: 64731
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
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First, always post a link or a clear reference to where you read something, then we can read the same thing and its context.

1) Threshold is internal, you don't have to know it
2) No, it has nothing to do with a MRU or LRU list
3) Blocks are there till they are not aged out. maybe seconds, hours, days, months. It depends on your activity.

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