3 Replies Latest reply: Dec 27, 2012 1:19 AM by DB RSS

    contents and working in buffer cache

    Santosh Pradhan
      Hi ,

      can anyone tell me wht is their exctly in db buffer cache , log buffer cache
      and what is the overall working of these in more more depth .(oracle 10g enterprise edition)

      thanx a lot in advance...........
        • 1. Re: contents and working in buffer cache
          sb92075
          user12045405 wrote:
          Hi ,

          can anyone tell me wht is their exctly in db buffer cache , log buffer cache
          and what is the overall working of these in more more depth .(oracle 10g enterprise edition)

          thanx a lot in advance...........
          Handle:     user12045405
          Status Level:     Newbie (15)
          Registered:     Feb 4, 2010
          Total Posts:     192
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          unwilling or incapable to Read The Fine Manual yourself?
          • 2. Re: contents and working in buffer cache
            Osama_Mustafa
            user12045405 wrote:
            Hi ,

            can anyone tell me wht is their exctly in db buffer cache , log buffer cache
            and what is the overall working of these in more more depth .(oracle 10g enterprise edition)

            thanx a lot in advance...........
            The buffer cache is part of the SGA. It holds copies of data blocks so as they can be accessed quicker by oracle than by reading them off disk.

            Refer to
            http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:907479900346445834
            http://www.exploreoracle.com/2009/03/31/database-buffer-cache/


            log buffer cache
            Each Oracle database has a redo log. This redo log records all changes made in datafiles.

            Refer to
            http://docs.oracle.com/cd/B19306_01/server.102/b14211/memory.htm
            • 3. Re: contents and working in buffer cache
              DB
              Db Buffer cache:_
              1.Duplicate copies of blocks from Datafile.
              2.it works according to LRU algorithm.
              3.It has three buffers pinned buffer,dirty buffer and free buffer.
              4.Dirty buffer contains the modified blocks which is ready to sent to Datafile.
              working:_
              1.whenever a transaction user establish it checks whether the corresponding blocks are here,if it is not it will reads from DataFile.
              2.It is write using DBWn and fetch using S.P


              Log Buffer:_
              1.It contains all changes of Database.
              2.Its main purpose is instance recovery and media recovery(if archive log enabled).
              Working:_
              1.All the changes are record in vectors(like insert,update,delete..etc) which is used to rebuild the structure.
              2.when 1/3rd full,1MB ,every 3secs,commit it will write to RedoLogFile.
              3.The LGWR process is used for write from RedoLogBuffer to RedoLogFile.
              4.Before commit it will write.


              Thank you,
              Regards,
              DB

              Edited by: DB on Dec 27, 2012 12:46 PM

              Edited by: DB on Dec 27, 2012 12:48 PM