SQL Server Performance

SQL Merge Replication

Discussion in 'General DBA Questions' started by P2003DBA, Dec 9, 2002.

  1. P2003DBA New Member

    Hi, I have read the information about Merge Replication but I can't quite understand how it works. If you have one data base go down, bring up the other database and allow updates to continue and then try to merge the two databases it says that you have to manually do the merge. Does anyone know what this means?
  2. bradmcgehee New Member

    I think we need more information. Why do you want to do merge replication? What is your actual goal?


    ------------------
    Brad M. McGehee
    Webmaster
    SQL-Server-Performance.Com
  3. P2003DBA New Member

    I'm responding to job requirements - I've been a SQL DBA for about 5 years, but never actually thought I had any reason to do merge replication - so I'm reading up on it and am not sure how stable it is - have you used it?
  4. bradmcgehee New Member

    Personally, I avoid using replication. I know others use it successfully, but I always look for other options, and there generally are. Replication, especially merge, can be complicated to set up, maintain, and especially hard to recover. The point of my questions were to find out why you wanted to do it so I could suggest an alternative.

    I am not familiar the specific question you asked about, do I can't address it, but perhaps others can. But if we can know more about the job requirements, then perhaps we can offer some alternatives (if they exist).






    ------------------
    Brad M. McGehee
    Webmaster
    SQL-Server-Performance.Com
  5. P2003DBA New Member

    Brad, I appreciate your insights into replication because they match my feelings too - it just seems very complicated and I wonder what kind of disaster recovery you would have to do for this type of configuration. I wish I had more information about this - I'm on the bench and get interview calls about replication. I can only tell them that I haven't done it but I've read about it - I was just trying to see if anyone else had used it and had some opinions about it -Thanks again -Pat
  6. HarryArchibald New Member

    I was new to MergeReplciation about a year ago. The company I work for now has about fifteen sites all connected by Merge Replication. The business requires that data is shareable in approximate real time across sites worldwide. Merge Replication is a good solution to this.
    The pros of it are that there are no comparable solutions, once established it has proven robust.
    The cons of it are that the documentation is poor, it needs to be managed and the path to reaching a robust solution was rocky.
    Overall, I would recommend using it but be aware that it is a complex solution.
  7. royv New Member

    I tend to stay away from replication and try to use log shipping. I am trying to convince the business minds here that we do not need it and can simply approximate real-time with log shipping. Unfortunately I have not seen log shipping being used where it gets called like every 15 seconds. Would be real interested to see if anyone has done this.


    "How do you expect to beat me when I am forever?"
  8. bradmcgehee New Member

    I think the best way to learn about replication is trial and error. You can perform virtually all replication functions on a single server (you don't need for than physical server). If you don't have access to a copy of SQL Server, you can get a demo copy from Microsoft's website for practice.

    In regard to royv, I have never seen log shipping used in such short intervals either. I would also be interested in hearing if anyone has tried this.


    ------------------
    Brad M. McGehee
    Webmaster
    SQL-Server-Performance.Com
  9. P2003DBA New Member

    Brad, log shipping looks a lot like Oracle's maintaining a stand-by data base in recovery mode. Essentially, there are two writes in Archived log mode (off-line logging) one to the tape and one to the standby database. If the primary database fails, the last on-line (redo) logs are flushed to the standby database and the standby database is then altered (by an sql alter database command) and made the active database. Of course you have to have multiple listners for this to work. Is this your understanding of how this works? If so, then yes, I think this would be a better solution than merged replicated databases. What does anyone else think?
  10. bradmcgehee New Member

    I have not used Oracle, but it sound similar in function to SQL Server log shipping. But again, it depends on your goal. In some cases, replication might be the answer, but in others log shipping, etc. Log shipping has been very reliable for us.


    ------------------
    Brad M. McGehee
    Webmaster
    SQL-Server-Performance.Com
  11. tkelley New Member

    Merge replication is a very nice process. In fact, I just set it up in SQL Server 7 replicating a database on our Intranet to a database on our Internet site. Once I determined how to make the connections through our firewall, the replication process if fairly simple and strait forward.

    Merge replication on pushes changes from the Publisher database to all of it's Subscribers. An important note to remember is that Merge replication changes the design of all of the tables in your database by adding a column called "rowguid". This change is made to both the Publisher and Subscriber.

    Try looking at the SQL BOL as to the steps in setting up the process. It works very well once you have your agents set up to run automatically. Let me know if you have any questions.

    *****
    MS, MCDBA, OCA, CIW
    *****

Share This Page