5 Replies Latest reply: Mar 22, 2013 1:12 AM by Lonion RSS

    SYNC or ASYNC

    998263
      Hi,

      When the network to the standby is lost with SYNC or ASYNC, where is the information queued and how is it retransmitted once the network has been re-established?
        • 1. Re: SYNC or ASYNC
          CKPT
          995260 wrote:
          Hi,

          When the network to the standby is lost with SYNC or ASYNC, where is the information queued and how is it retransmitted once the network has been re-established?
          Once the network is reestablished and if there are any more archive gaps, of course the FAL parameters also plays key role to fetch the GAP's.
          • 2. Re: SYNC or ASYNC
            Mihael
            archivelogs on primary site
            • 3. Re: SYNC or ASYNC
              Hemant K Chitale
              Oracle continues generating ArchiveLogs on the Primary. These are sent to the Standby when the connection is re-established.

              Note : In MAXIMUM PROTECTION mode, with SYNC, if the connection fails, the Primary database halts.


              Hemant K Chitale
              • 4. Re: SYNC or ASYNC
                Hemant K Chitale
                The Primary continues generating ArchiveLogs which are sent to the Standby once connection is re-established.

                Note : In Maximum Protection mode, with SYNC, a network disconnect will cause the Primary to halt.


                Hemant K Chitale
                • 5. Re: SYNC or ASYNC
                  Lonion
                  about this ,Larry Carpenter's book "Oracle Data Guard 11g Handbook" has a best description , i post it here :

                  Automatic Gap Resolution

                  A log file gap occurs whenever a primary database continues to commit transactions while the LNS process has ceased transmitting redo to the standby database.This can occur whenever the network or the standby database is down,depending on how you have chosen to implement your Data Guard configuration.While in this state,the primary database LGWR process continues writing to the current ORL,fills it,and then swithes to a new ORL while an archive(ARCH) process archives the completed ORL locally.This cycle can repeat itself many times over on a busy system before the connection between the primary and standby is restored,creating a large log file gap.

                  Data Guard uses an ARCH process on the primary database to continuously ping the standby database during the outage to determint its status.When communication with the standby is restored,the ARCH ping process queries the standby control file(via its RFS process) to determine the last complete log file that the standby received from the primary database.Data Guard determines which log files are required to resynchronize the standby database and immediately begins transmitting them using additional ARCH process.At the very next log switch,the LNS will attempt and succeed in making a connection to the standby database and will begin transmitting current redo while the ARCH processes resolve the gap in the background.Once the standby apply process is able to catch up to current redo records,the apply process automatically transitions out of reading from archived redo logs,and into reading from the current SRL(assuming the user has configured Data Guard real-time apply).One last side note:beginning wiht Data Guard 10g,one ARCH process at the primary database is always dedicated to local archival to ensure that remote archival during gap resolution does not impact the ability of the primary to recycle its ORLs.