manish hoiyani

• Sep 18th, 2006

 

Database buffers:? It stores the most recently executed? blocks and apart from that, it stores the rollback blocks? which contains the previous record for those rows which have been updated.

Buffer also stores the dirty blocks means blocks?which contains the new updated value which has been not yet committed by the user.

Mohammed Abdul Afroze

• Oct 5th, 2007

 

Buffer Cache Stores the most recently used blocks of data. It can also have modified data that has not permenently written to disk. When a row in?a table is updated the foreground server processes reads the datafile information on the disk in to the buffer cache. Hence modifying the data block in server memory. Oracle writes the block from the buffer cache to the LRU(Least Recently Used) Mechanism.

taya_ronak

 Profile Answers by taya_ronak 

• Feb 2nd, 2009

 

Database buffer contains the data which server process reads recently from disk.


Database buffer may have three parts:
1. free buffer
2. dirty buffer
3. pinned buffer


Free buffer area is free to be used to store data.

Dirty buffer area contains the data which is updated since read from disk, but not written to the disk till now.


Pinned buffer is a area where processing on specific data for current transaction is going on.


Database buffer may be of three types:
1. keep
2. recycle
3. default


Database buffer may be divided into five different block size buffers:

2k,4k,8k,16k,32k and 64k also but supported by most of the servers (HP, IBM AIX, SOLARIS 10)

saihaan

 Profile Answers by saihaan 

• Jul 2nd, 2009

 

Database buffers consists of the dirty blocks. When ever we are trying to update some table/etc. First it verifies whether the data exists in database buffer , If not it fetches the information from data files to database buffer. So the modified values exists in db buffer until a check point
occurrence. When the transaction is committed then the dirty blocks/modified blocks will be written on to the data files with the help of a db writer. If the transaction is not committed/rolled back then the data from the undo segment will be moved to data files.

What ever
SQL statement that is executed, it checks in db buffer before retrieving the data from data files.

NAGARAJ OCP

• Dec 27th, 2011

 

Database Buffer cache has four states:

Pinned: multiple sessions are kept from wirting to same block @ same time. Other session waits to access these blocks
Clean : Now the session is unpinned
Free or unused its happens @ instance startup or its indicate data buffer cache is clean
Dirty happens when datas are modified, needs to written to disk