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    Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?

    GTS (DBA)

      Good Morning to all ;

       

      I am getting bit confused from oracle official link . REF_LINK : Log Apply Services

      Redo data transmitted from the primary database is received by the RFS on the standby system ,

      where the RFS process writes the redo data to either archived redo log files  or  standby redo log files.


      In standby site , does rfs write redo data in any one file or both ?


      Thanks in advance ..

        • 2. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
          Baris Yildirim

          Hi,

          Yes RFS can write both. if a gap exists RFS writes archived log, if not standby logs.

           

          Regards

          • 3. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
            GTS (DBA)

            Hi  Baris ;

             

            Thanks.  Now i have problem with some other  things.

            Later we 'll continue this task .

            • 4. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
              Baris Yildirim

              Hi

               

              you're welcome.

               

              you can always ask me my friend.

               

              Best regards

              • 5. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                teits

                Hi,

                 

                In standby site, RFS process can writes to standby redo log OR archive redo log.

                The RFS process writes to an archive redo log file if any of the following conditions are met:

                1.There are no standby redo logs.

                2.It cannot find a standby redo log that is the same size as the incoming online redo log file.

                3.All standby redo logs of the correct size have not yet been archived.

                 

                senario 1:

                In SYNC redo transport mode, when RFS writes to standby redo log, LNS process(in primary DB) send 1MB(upper limit) of redo data over the network multiple times. in this case RFS always write to standby log files except there is a redo gap to resolve.

                Redo log file(primary)===>LNS ===>RFS===>standby redo log file

                 

                senario 2:

                ARCH process(on primary DB) read 10 megabytes from the local archive log and issue a network send to the RFS process on the standby, the RFS process receives the redo sent by the ARCH process and performs I/O into either the standby redo log or archive redo logs e.g if there is no adequate standby redo file in standby DB, RFS process write into archive log file.

                Archive log file====>ARCH===>RFS====>[archive|standby log files]

                 

                check: LGWR , ARCH , LNS resposiblities in dataguard very good posts

                 

                HTH

                Tobi

                • 7. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                  GTS (DBA)

                  Hi tobi ;

                   

                  You are almost welcome to answer.

                   

                  teits wrote:

                   

                  In standby site, RFS process can writes to standby redo log OR archive redo log.


                  The RFS process writes to an archive redo log file if any of the following conditions are met:


                  1.There are no standby redo logs.

                  2.It cannot find a standby redo log that is the same size as the incoming online redo log file.

                  3.All standby redo logs of the correct size have not yet been archived.

                   

                   


                      What do you mean here ?

                    

                      Cannot find a standby redo log that is the same size as the incoming online redo log file


                     Do you mean standby redo log file size must be same as ' Primary database online  redo log file ' ?


                     I mean if primary db redo log file size is 50m , what would be size of standby redo log file ?


                     is it same as 50m 0r anysize ??? Please discuss in detail ...



                  Thanks

                  • 8. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                    teits

                    Hi Gts,

                     

                    yes. at least the size of the largest redo log file in the source primary DB should be equal to the smallest standby redo log files on the standby DB.

                    ANOTHER condition: you should have an additional standby redo log files in standby DB. e.g primary have 4 redo log files, standby should have at least 5 redo log files

                     

                    to better easy your DBA work. let all your redo log files and standby redo log have the same size.

                     

                    HTH

                    Tobi

                    • 9. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                      GTS (DBA)

                      Hi Tobi ;

                       

                      Thanks.  Again little confusion ..

                      teits wrote:

                       

                      at least the size of the largest redo log file in the source primary DB should be equal to the smallest standby redo log files on the standby DB.

                       

                       

                      Primary & standby log file size should be same - this is okay.

                      1) what are trying to disclose about  largest & smallest here ? -  You are confusing.

                      2) what abt group members ? should be same as primary or need  to add some members additionally. ?

                       

                       

                      All standby redo logs of the correct size have not yet been archived.


                        - at this situation , can we force on standby site ? any possibilities ?

                          

                      • 10. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                        teits

                        Hi GTS,

                         

                        GTS (DBA) wrote:

                        Primary & standby log file size should be same - this is okay.

                        1) what are trying to disclose about  largest & smallest here ? -  You are confusing.

                         

                        Read: http://docs.oracle.com/cd/E11882_01/server.112/e25608/log_transport.htm#SBYDB4752

                        "Each standby redo log file must be at least as large as the largest redo log file in the redo log of the redo source database. For administrative ease, Oracle recommends that all redo log files in the redo log at the redo source database and the standby redo log at a redo transport destination be of the same size."

                         

                        GTS (DBA) wrote:

                        2) what abt group members ? should be same as primary or need  to add some members additionally. ?

                        Data Guard best practice for performance, is to create one member per each group in standby DB. on standby DB, one member per group is reasonable enough. why? to avoid write penalty; writing to more than one log files at the standby DB.

                        SCENARIO 1: if in your source primary DB you have 2 log member per group, in standby DB you can have 1 member  per group, additionally create an extra group.

                         

                        primary

                        standby

                        Member per group

                        2

                        1

                        Number of log group

                        4

                        5

                         

                        SCENARIO 2: you can also have this scenario 2 but i will not encourage it

                         

                        primary

                        standby

                        Member per group

                        2

                        2

                        Number of log group

                        4

                        5

                         

                         

                        GTS (DBA) wrote:

                        All standby redo logs of the correct size have not yet been archived.


                          - at this situation , can we force on standby site ? any possibilities ? 

                        you can not force it , just size your standby redo files correctly and make sure you don not have network failure that will cause redo gap.

                         

                        hope there is clarity now

                         

                        Tobi

                        • 11. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                          GTS (DBA)

                          Hi Tobi ;

                           

                          From all your replies , i need to clarify few things ...

                          because  oracle did NOT explain impacts of performance ( if we configure against ).

                          I am very sorry for disturbing you.

                           

                          Ex : Please assume  , As per your suggestion , i have configured  dr following  below :


                          Oracle recommends that all redo log files in the redo log at the redo source database and

                          the standby redo log at a redo transport destination be of the same size."


                          In primary  DB ,

                           

                          SQL> select GROUP# , MEMBERS , bytes from v$log;


                              GROUP#     MEMBERS      BYTES

                            ---------- ---------- ----------

                                   1         2     20971520   --->  20m

                                   2         2     20971520   --->  20m


                          In standby DB ,

                           

                          SQL> select GROUP# , MEMBERS , bytes from v$log;

                           

                              GROUP#    MEMBERS      BYTES

                            ---------- ---------- ----------

                                   1        1     20971520      ---> 20m 

                                   2        1     20971520      ---> 20m 

                                   3        1     20971520      ---> 20m

                           

                          Question


                          If  standby redo log file size is  larger than  source database (primary) log file size   --

                            (standby log file size is 30m ,  primary database logfile size is 20m )

                                          

                               1) What is the major impact here ? 

                              

                          Standby redo log file must be at least as large as the largest redo log file in the redo log of the redo source database

                           

                                I am getting confusion - please show me simple example ?



                            Thanks in advance ..

                          • 12. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                            teits

                            Hi Gts,

                             

                            Answer to 1) unused disk space. Redo log will only fill 20mb out of 30mb of standby redo log

                             

                            2) in your example, all standby log files are larger than redo log files. That is the requirement.

                            If two of your standby is 15mb that means, it will not meet standby configuration requirement.

                            The smallest of the standby log file is NOT as large as the largest redo log file.

                             

                            HTH

                            Tobi

                            • 13. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                              GTS (DBA)

                              Hi Tobi ;

                               

                              Thanks for your previous reply.

                               

                              teits wrote:

                               

                              check: LGWR , ARCH , LNS resposiblities in dataguard very good posts

                              Some links are saying LGWR &  ARCH  both  sending redo information  to standby database.

                              but you say LGWR never send redo information to standby destination.  ( from above link , you  replied to OP question)


                              REF_LINK :  How REDO data is SENDData Guard | Raheel's Blog

                              REDO data is send either through ARCn process or LGWR proces


                              1) How do we know redo transport  information is done by LGWR or ARCH  to standby database ?  Can we check it ??

                              2) If possible , please show it. Could you please show simple example  ?

                               

                              Thanks in advance ..

                              • 14. Re: Where RFS exactly write redo data ?  ( archived redo log or standby redo log ) ?
                                Baris Yildirim

                                Hi,

                                 

                                on primary, log_archive_dest_n parameter's value (for standby) says to you which process is used.

                                 

                                select name,value from v$parameter where name like'log_arhive_dest%';

                                 

                                You can see LGWR or ARCH in the value.

                                 

                                Best Regards

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