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  1. #1
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    Network Replicas (97s2)

    Hi friends,
    I have just rolled out an application that (sort of) acts like a punch clock. Users enter some key data, click "Start Time", finish the job and click "End Time". About 150 employees have a copy of this on thier C: drive, with linked tables to the back end version on the network.
    There will be 1 or 2 upgrades going out in the future, with some bug repairs.
    Would a design master and replicas for the users enable me to easily upgrade the app and avoid having the users recopy the new version locally? Are there troubles to plan for?
    As always, thanks in advance for your help, DP

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    Re: Network Replicas (97s2)

    You will have some issues to deal with in rolling out changes and enhancements. Replication can work, but there's a good deal of pain and overhead with it. For one thing, keeping track of 150 different replicas is no mean feat. Furthermore, if someone decides to rename a directory, you have complications to resolve. And finally, it adds a fair bit of overhead if data tables are involved. That not withstanding, it is the right solution in some situations, especially if you have a loosely connected network.

    In the past we have used a login script to copy the latest version of things like the database front-ends, or the security file for secured databases. However, for 150 users, that will put a significant load on your network and on the server. More recently, we developed what we refer to as a Database Launcher. It checks to see if the user has the latest version, and only downloads if the version needs updating. This general approach assumes of course that no local tables exist, and that users are not adding their own objects to the front-end database. Replication does deal with that situation more gracefully.

    A final comment/question. I am assuming that the back-end is also Access. If that is the case, and there is any significant data entry effort, you are likely to have multi-user issues (record locking), and performance is likely to be a problem. On the other hand, if it is truly a punch-clock application where people make just a few entries each day, you may be in good shape. Hope this rambling helps.
    Wendell

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    Re: Network Replicas (97s2)

    Wendell, Thanks for the response. I believe I have started this project in the best way. All users have thier version in a like named folder at the root of thier workstation C: drive, so the only network traffic is thier single records heading to the data version linked tables. No user will be adding or modifying the version they work with. The data version (located on a secured network drive) can only be accessed by a few of the administrative staff, and even then only to analyze the data. I am the entire MSAccess department (which is sometimes good, sometimes bad !!), so I have control over any design changes.
    The answer I am searching for is, will I be able to roll out the next version as one DM and have the users copy and paste the replicated version locally, and then be able to add to the DM and synch all of the users local copies? I hope I have explained it well enough. Thanks again, DP

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    Re: Network Replicas (97s2)

    I understand about being the entire IS staff - been there, done that, sometimes fun, sometimes sheer terror.
    If you actually use replication, and create a design master of your front-end, then you can't simply copy and paste. You have to actually use the the Replication/Synchronize Replicas command in Access. It can be done either from the workstation copy (so users could do their own), or you can do it from the Design Master. In any event, each workstation would have to have a network share that can be seen from the location of the Design Master. An automated alternative for one of our clients was a tool called Replication Manager that could be used to schedule replication updates, but as far as I know it's no longer available, as it came with the Developer version of Office 97. I think I would start with just a simple copy and paste approach and see if that will work. You will be dependent on the users to "download" a new version to their workstation when they are supposed to (unless you want to do it 150 times), but that beats going to every workstation to create a network share, and then teaching users how to do thier own replication. In that scenario, you actually replace their entire database, while in replication, it simply adds or replaces objects in the database. Does anybody out there have a different opinion?

    You didn't indicate how many records a typical user would be entering during a day, or how critical the data is, but you should be concerned about a backup strategy for the data. Access isn't the most reliable database out there, so you will probably want to create a backup two or more times a day.
    Wendell

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    Re: Network Replicas (97s2)

    I do not hink there is need for the rep mgr tool. I am aware of it , but there should only be 2 or 3 more versions at most. The app will recieve @ 2000 records a day(total), which I realize will become a monster very quickly. The data is very critical because it will be used for incentive calculations and department performance evaluations. I do have a data archive routine that will run weekly, and a VB6 file backup routine that will run at least daily, so I am confident that is covered (in addition, there is a network backup every night at midnight).
    As I have been testing this morning, I do like the replica sync way. If I have quickly learned correctly, I am thinking once the user has the app local, the team supervisors can go to each workstation (when an update is rolled out) and sync from the user copy to the DM on the network, as opposed to me using the DM to sync to them. How's that for quality work before 8 am???!!! Let me know your thoughts....Thanks, DP

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    Re: Network Replicas (97s2)

    If you're talking about front-end replication, my recommendation is don't. I have done it, but it requires a great deal of care and feeding and frequent rebuilding of design masters when they blow up. You can't simply hang a new design master out there, either. You have to modify the current design master and then have your users sync their replicas to it, or at least to the replica they were created from. You will have problems with multiple back ends in a replicated front end, and you will have to replicate both front and back end, even though the back end lives on the server. Any local tables in the front end will return to haunt you unless you only allow changes from either the design master or the replicas. Otherwise, you will run into data conflicts in the sync and you'll have to untangle those is the messiest possible ways.
    Charlotte

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    Re: Network Replicas (97s2)

    Charlotte, Thanks again for the insight. I have decided to just hammer out a quick VB routine to filecopy the new release to the local directory of each user, which I will distribute together. HOWEVER, I did create a quick test dbase to play with the master and replica function, and now every existing database on my PC has all of the system tables. Have you seen this? From another employees PC, the apps residing on the network do not show these system tables, but when I open them, they do. Are these tables actually in existence, and can I get rid of them? I have deleted my test, but the system tables still appear (they have no data and cannot be opened, but trying to delete them gives me a "permission" type of error. Thanks again, DP

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    Re: Network Replicas (97s2)

    The advantage of the replication manager is that you can schedule an automated update when you have a change you want to deploy. However your scheme should work - you are putting the responsibility on the team supervisors. Note however the issue with having a C-Drive share on each workstation that must be setup, and the problem of workstation, directory and file name changes that cause replication to fail. I should also note that one of our clients with 120 workstations used replication for a while, and then went to the file copy route because of the administrative issues. If you get to that point, we may be able to help you.

    As to the back-end reliability and capacity issues, if you are using a simple record structure with no memo fields, you should have reasonable reliability. The major corruption issue is when someone crashes their workstation in the middle of adding a record, and it seems to happen more frequently when memo fields are involved. On the other hand, since your data is fairly critical, you might want to consider a more robust back-end such as SQL Server. If your server hard drive crashes at noon, can you get by without the data that was entered from early morning to noon?

    Another issue you may face is page locking when two or more people try to add a record to the same page at the same time. Access 97 made some improvements in that area, but Access 2000 or SQL Server are much better at it. As to size, if your average record size is 100 btyes, in 100 days you would have a database that is about 20MB. Access 97 has a size limit of 500MB I believe - can't check it as we are on 2000 here but look under specifications in the help. So you should be OK for 2 to 3 years.
    Wendell

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    Re: Network Replicas (97s2)

    Thanks Wendell, any thoughts on these darn 'ghost' system tables i am referenceing in my previous post?.....

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    Re: Network Replicas (97s2)

    Charlotte, Wendell and all,
    Ignore my "ghost" system table posts. <img src=/S/brickwall.gif border=0 alt=brickwall width=25 height=15>...I forgot to turn off the options to show system objects.....at least I got todays oops out of the way.....the rest of the day should be just terrific....Thanks for all, DP

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    Re: Network Replicas (97s2)

    I'll reply even though you said not to worry. Replication adds some fields to every table in your database (including the system tables). The only way to get rid of them is to import all the objects but tables from your replicated DB (Design Master) to a new empty database. For non-system tables, you will have to manually remove the replication fields. If it gets sticky, there is a KB article on the MS site that tells you how to remove replication from a database. I guess I'm not quite as negative about replication as Charlotte, but it can be a major <img src=/S/devil.gif border=0 alt=devil width=15 height=15> to work with. Good luck.
    Wendell

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    Re: Network Replicas (97s2)

    What exactly do you mean by the "system tables"? Which system tables? All your databases have system tables, but you can only see them if you have that option turned on. Are you talking about something different?
    Charlotte

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    Re: Network Replicas (97s2)

    One thing I sometimes do is to provide the entire app startup as a C++ exe. (You could use a VB exe equally well.)
    This stub checks the front-end for a version number I store in a table and the server. If the server has a front-end with a newer version then it copies it across.
    It then checks table linkages and re-links if it can do so automatically.
    It then starts the Access front-end. Also I can then use Access security to protect the whole front-end because this stub program will launch Acces with the necessary workgroup/user/password.
    All of this is transparent to the end-user.

    In the past I have provided a small routine to copy across a newer version, usually the user didn't use it EVEN when told there is a newer version to copy across.

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    Re: Network Replicas (97s2)

    Andy,Charlotte and Wendell, Thanks again for the expertise....

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