About replication

  • Vladimir Ilnitsky

    At Acculturation CD there is the good example of databse replication when one database is in Honolulu and other database in Ghanzi.
    Does anybody know:
    1. Can both scripts (the "primary_start" and "secondary_start") be launched simultaneoushly? I.e. can I start "primary_start" and "secondary_start" (without primary_stop before) for Honolulu if I don't know what scripts launched in Ghanzi in this time?
    2. Can I add additional database (in London, for example) and built replication circuit for three or more databases? I.e. have in work in the same time one script "primary_start" and several "secondary_start" for each database?

    • K.S. Bhaskar

      K.S. Bhaskar - 2008-05-20

      1. Yes, primary start in Honolulu and secondary start in Ghanzi can be launched simultaneously.  As a practical matter, the secondary listens at a TCP port and the primary is told at which IP address and TCP port it should make a connection attempt to find the secondary.  If the primary comes up first, and there is no secondary, it simply tries again and keeps trying every few seconds till it connects.  But out of considerations for practicality and prudence, it is a good idea to stop the old primary before starting the new primary, and to otherwise ensure that only primary is active at any given instant in time.

      2. Current releases of GT.M support up to 16 secondary instances, each of which can replicate to 16 tertiary instances (for a total of 256 tertiary instances), and so on without any limit imposed by GT.M to the number of levels.  However, the Acculturation live CD was created when GT.M only supported one secondary instance, and the exercises therein only deal with one secondary instance.  A future edition of the Acculturation live CD will have exercises with three instances (maybe Philadelphia, Manila and Cape Town).  Meanwhile see http://www.fidelityinfoservices.com/user_documentation/Replication/GTM_Multi_Site_Replication.html for a technical bulletin on multi-site replication.

      -- Bhaskar


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