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  1. #1
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    Replication (A97-SR2)

    I am starting to experiment with replication. I am doing all this at home on a couple of networked PCs.
    I have created a database and made it the Design Master, this database is split into a FE/BE. From the FE Design Master I have created a replica (R1 is replica 1) on the same PC. From the FE replica I have created another replica (R2) on another PC.
    When I add data (on FE R2), I don't see the data in R1. When I go into Synchronise New on FE R2 to synchronise with FE R1 it allows me to do it, but after it I don't see any data changes on R1.

    When you add a replica I assume you do it from the FE and not the BE?

    Also when you synchronise do you also do it from the FE rather than the BE?

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    Re: Replication (A97-SR2)

    OK Pat, don't laugh that I'm responding to this but I'm trying to learn from your problem and want to be sure I'm following the train of thought before Han's answers <img src=/S/compute.gif border=0 alt=compute width=40 height=20> with the fix!!

    I'm assuming that by BE you mean the tables are split??? The reason I ask is because we have a database at the office with split tables. The Master database resides on the server with these tables. 4 different workstations have copied versions fo the Master database residing on their workstations. All 4 point back the split database. As far as I know all four have been saving data to the split tables on the server without any issue. Am I missing something?? Hans??????

    Leesha

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    Re: Replication (A97-SR2)

    Pat,

    Save yourself a LOT of headaches and don't try replicating the front end. Trust me, I've done it and it requires too much maintenance to be practical. The customary method is to replicate the back end and then use local replicas as backends to local copies of the front end. When you sync the backend replicas, the data will be merged according to the rules you've established.

    One of the things to keep in mind about replication is that it takes place in an established order. First all the design changes are replicated and then the data changes are replicated, so be advised and avoid changing table structures and data in the same sync, especially if some of those changes rename or delete fields.
    Charlotte

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    Re: Replication (A97-SR2)

    I agree with Charlotte - replicate only the back-end and not the front-end. I worked with a replicated front-end for two or three years, and it was a pain. It did work, but the maintenance of it was an ongoing challenge. The Microsoft party line is that a replicated front-end is a slick way to distribute design changes to users, but in my experience you are better off to completely replace the front-end than to try to replicate it. On the other hand, when you have intermittent connectivity (i.e. a traveling salesman application), then replicated back-ends can work really well.
    Wendell

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    Re: Replication (A97-SR2)

    Thanks Charlotte.

    When you replicate the backends, do you do create the replica from the backend? When you synch the backend, do you do it from a replicated backend?

    >>The customary method is to replicate the back end and then use local replicas as backends to local copies of the front end.
    What do you mean by this statement? I'm sorry, I can't understand it. Do you mean that you replicate the backend but only update the frontend by copying the source of the front end?

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    Re: Replication (A97-SR2)

    Thanks Wendell

    See response to Charlotte.

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    Re: Replication (A97-SR2)

    Hi Pat,

    I don't know much about replication - I didn't like the results of some tests I did and never tried again - but perhaps the attached picture will clarify some things.

    You can replicate the back end, then put replicas of the back end on different computers. The replicas will synchronize with the master back end database.

    The front end is not replicated; just give each user a straight copy of the front end database, and link the tables to the appropriate back end. If you make design changes to the front end, just distribute fresh copies and replace the old version by these copies. So changes in the front end are not distributed by replication, but by copying the entire front end.
    Attached Images Attached Images
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    Re: Replication (A97-SR2)

    >>You can replicate the back end, then put replicas of the back end on different computers. The replicas will synchronize with the master back end database.
    I thought you had to replicate a back end to a destination via the "Create a Replica" command, not by just copying the replicated backend.
    Do you create a replica from the BE? I would have thought so.
    Do you synchronise backends from a replicated BE? Again, I would think so.

    I understand the FE idea, it's the same as when you are not replicating, in the distribution thereof.

    Thanks Hans.

  9. #9
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    Re: Replication (A97-SR2)

    Hi Pat,

    Yes, you make replicas from the original back end database. If you have Office Developer Edition, you can use the Replication Manager as a convenient interface to create and manage replicase, set synchronization schedules, etc. But, as I mentioned, I don't have much experience with this, so if you have more specific questions, others Loungers will be able to give better answers than I can.

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    Re: Replication (A97-SR2)

    Hi Hans
    I have Office Developer for Office 97 but only the Premium version for Office 2000.
    For someone who doesn't know much about replication you certainly know a bit about replication. (that doesn't sound right, does it?).

    I will go away, armed and dangerous, and give this a burl. Thanks for your time, you too Wendell, Charlotte.

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    Re: Replication (A97-SR2)

    Actually, it's safer to use a replica to make other replicas rather than creating them all from the design master. That gives you a fallback position when (not if) the design master or the intermediate replica goes sideways.
    Charlotte

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    Re: Replication (A97-SR2)

    It looks like you pretty much have your arms around this. You are correct that you want to create the replica using the Create a Replica command - simply copying the BE database won't work. There are a few oddities that occur with a replicated BE. Probably the most annoying is that you can see the replication fields from the FE (but not the BE), so you probably want to keep users out of the tables. Another thing is that the syncronization must be done from the back-end, so users have to be trained to open the back-end to do that specific task - unless you use replication manager. Replication can get messy over the long haul as network connections change and it gets difficult to get rid of unused replicas. Finally, conflict management gets to be a problem if you are using autonumber fields - either only one user should be allowed to add records, or you will want to switch to random rather than incrementing. We have a Colorado client who has an employee who lives in Arizona and does phone work for them, and they create a replica to a CD-ROM and mail it back and forth, but it requires lots of discipline to make it work. On the other hand they also travel all over the world doing seminars and carry a copy of their contacts database on a laptop, and that works pretty well. We have links to several articles about replication on our web site. Also note that 2000/2002 has a bit more robust replication facility that 97. Hope this helps.
    Wendell

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    Re: Replication (A97-SR2)

    Thanks Charlotte re the creating replicas from replicas vs Design Master.

    Thanks Wendell for your comprehensive summary of what I was trying to get my head around.

    If you are using A2k can you load the Replication Manager from the MS web site?

    >>Another thing is that the syncronization must be done from the back-end, so users have to be trained to open the back-end to do that specific task - unless you use replication manager.
    Can synchronisation be done from code in another database targetting one of the replicas?

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    Re: Replication (A97-SR2)

    <<If you are using A2k can you load the Replication Manager from the MS web site?>>
    Not as far as I know - you have to try to find a copy of the Developer version of Office 2K. And that's really a problem if you are trying to get a copy of the 97 version of Replication Manager. One of our clients used replication manager briefly to distribute changes to a front-end used by about 80 users, but they eventually figured out that was more bother than it was worth. The only scenario I've seen where it really makes sense is if you have lots of geographically remote locations with simple dial-up connectivity. An example might be convienence stores where you have lots of them reporting to and getting data from a central location.

    <<Can synchronisation be done from code in another database targetting one of the replicas?>>
    You can use the JRO to do replication tasks, though I haven't had any personal experience with it (and don't want any either!). However I'm not sure you can do it from something other than another replica. There was a recent thread on this subject where they wanted to use their own conflict resolution procedure. The best stuff I've seen on programming the replication functions is in the Access Developer's Handbook.
    Wendell

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    Re: Replication (A97-SR2)

    Just to add my $0.02 to the good advice already given. I wholeheartedly agree with the advice NOT to replicate the frontend.

    Replication *will* change any autonumber fields from incremental to random, so your users may become confused if they are used to seeing sequential numbers. The solution is to create your own function for generating "pseudo-keyfields" that the users see.

    The Replication Manager included with the office developers edition allows you to do "indirect" synchronizations which are much more robust over a WAN than direct synch's. You are highly advised to use indirect synch on a dial-up connection. Direct synch will eventually corrupt your database.

    Do not consider moving files back and forth via (say) email if they are part of a replica set. Once a file is in place, only move it using Replication Manager, not Windows Explorer. Moving a file will eventually lead to problems.

    Use replica farms to increase the fault-tolerance of your replica set. Described on the web site below.

    The best source of information that I have found for replication is at www.trigeminal.com.
    --------------------------------------------------
    Jack MacDonald
    Vancouver, Canada

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