Saturday , November 25 2017



To overcome  instance level failovers oracle as introduced multi instance database , which is nothing  but RAC  database .

RAC  supports  two  types of failover’s:

1 . session failover

  1. select failover


  • There is no concept of DML failover in RAC system.
  • Various technologies that are including under MAA  are :
  1. RAC
  3. ASM

Oracle as redefined the term  High  Availability to MAA



Data guard  is meant  for DISK OUTAGE (or)  SITE OUTAGE. Data guard  is a disaster Recovery solution. Data guard   alone   are in combination with   RAC  provides a Robost  high availability solution.

  • Prior to 9i, data guard  is called are standby
  • In version 9i, oracle as made lots of architectural changes to its high availability technology and rename the technology as dataguard.

There are two types of stand by

  1. Logical standby
  2. Physical standby


  • Logical standby uses the concept of SQL apply and it is generally used for Reporting purpose.
  • Data guard are physical  stand by there is also called as Replicating Technology. It is  Replicating the data.
  • If we want have a business continuity plan and disasters continuity solution, we need to configure physical stand by.
  • If we configure physical standby with “ data guard broker”  then we call the configure as data guard .
  • Prior to 9i configuration mode is called delayed production mode.


  • In delayed production mode , archiver  background process takes the responsibility of shipping the generated archivelogs to the physical standby.
  • RFS (remote file server ) reads vector by vector and constructs Archive logs .
  • Then constructed archivelogs will be picked by MRP (manage Recovery process) and apply’s the data to the physical stand by if it runs in MRM mode(Manage Recovery mode)
  • Physical standby may run either in MRM mode or READ ONLY MODE.
  • In the industry , Some times we open  the physical standby in READ ONLY MODE to generate the resource intensive reports.( off loading the primary).
  • In the above architecture there will be lot of “ data divergence” (miss match) between the primary and physical standy
  • In the industry we are going to maintain the physical stand by exatly  replic  off primary database. We are going to the physical stand by in remote geographical.


  • In order to minimize data divergence , oracle as introduced “LNS” ( log network service).
  • LNS sucks data either from  Redo buffer cache (or) from online Redologs and shift’s  the data to the  physical standby
  • Whenever there is an Archive log gap , RFS  pings  back  the primary Archiver to shift the Archive log  to the physical stand by.
  • With the above Architecture ,we can minimize data mismatch, but we cant achicve “ A NO DATA LOSS  SOLUTION”.


  • In order to achive no data loss solution oracle as introduced  stand by  redo logs  which needs to be  created at the physical standby .
  • The size of standby redo logs should be same as the size of primary redologs.
  • In the above architecture , user gets commit complete acknowledgement , once the data as been returns to the primary redo logs as well as the stand by redo logs.
  • If primary is unable to send the data to at least one stand by , primary goes down
  • The no. of stand by redo logs that we need to create are

(max no. of redo logs  per thread +1)*( max no. of thread)

(2+1)* 1 =3

  • Thread is nothing but
  • The above configuration mode is called maximum protection  mode .
  • With the above architecture , we can achive  NO DATA LOSS SOLUTION   .



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