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MS Access Forum / Replication / September 2003

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The Art of Replication Farming

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JD Kronicz - 23 Sep 2003 16:16 GMT
First I would like to that Michael Kaplan and Jack
MacDonald for the information they have bestowed upon me
directly or indirectly (no pun intended) thorough others
postings on the newsgroup.  My understanding is still
incomplete as I approach my first attempt at doing this in
the real world.  I was hoping to get a few more thoughts
on my proposed conversion to a farm topology beform
implementing it (measure twice and cut once).
Current setup:
1. A design master sitting on a server on a wan
2. A replica on each of the client pcs on the lan (why are
there replicas on each client on the lan? ... because they
substantially improved the performance for folks on the
lan)
3. A replica on each of the client pcs which access the
server via wan.
4. In code each of the replicas is synchronized directly
with the design master via JRO upon startup and shutdown
of each replica.

Problems with the currect design ..
1. occasionally the design master becomes incommunicable
for syncs and some intervention needs to be taked to
repair it.
2. I gather the setup violates some established principles
for good design of a replication stategy

Proposed Design:
1. A farm consisting of three replicas all sitting on a
share on a spare machine on the lan.  RepMan would manage
this set.
2. A replica would reside on each user machine whether
they are on the lan or on a wan connection.  RepMan would
also be on each machine and manage the local copy.
3. Indirect synchronizations would be initiated from the
replicas via their local synchronizer with the farm.
4. The design master would stay on the server and be
unmanaged.

Proposed conversion process:
1. Create a share on a spare machine on the lan
2. Install rep man on the machine.
3. create three replicas on this machine and manage them
via repman.
4. Install repman on each machine with a replica.
5. Remove JRO code which currently causes direct syncs
with the design master.
6. Use the client copies of repman to establish a schedule
for indirect syncs of the local managed replica with the
farm.

Questions:
1. It this reasonable?
2. The local replicas on the client machines will not be
visible to the farm or the rest of the network.  However,
since the syncs will be initiated from the client machines
is this necessary?  It seems that the drop box might need
to be visible .. but could this reside on a network server?
3. This is a more fundamental question ... I am still not
sure I understand why indirect syncs are important.  I
understand how the farm can repair itself and bring
members that have been labels unavailabe for syncs back
into the loop.  Is it that indirect synchronizations
minimize the problems that the self repairing properties
of the farm correct?

Thanks

JD
Michael \(michka\) Kaplan [MS] - 23 Sep 2003 17:41 GMT
"JD Kronicz" <jkronicz@gfnet.com> wrote...

> Proposed Design:
> 1. A farm consisting of three replicas all sitting on a
> share on a spare machine on the lan.  RepMan would manage
> this set.

Wrong -- they are not on a share. If you share them out then you will end up
with direct syncs. Just have a dropbox that does not contain the replicas
and let the synchronizer worry about applying the changes.

> 2. A replica would reside on each user machine whether
> they are on the lan or on a wan connection.  RepMan would
> also be on each machine and manage the local copy.

Yes.

> 3. Indirect synchronizations would be initiated from the
> replicas via their local synchronizer with the farm.

Yes.

> 4. The design master would stay on the server and be
> unmanaged.

Well, it would not necessarily be on the server, would it? Why not on the
dev's local machine?

> Proposed conversion process:
> 1. Create a share on a spare machine on the lan
[quoted text clipped - 7 lines]
> for indirect syncs of the local managed replica with the
> farm.

Everything except for #1 about the replicas in the share looks fine.

> Questions:
> 1. It this reasonable?

See above.

> 2. The local replicas on the client machines will not be
> visible to the farm or the rest of the network.  However,
> since the syncs will be initiated from the client machines
> is this necessary?  It seems that the drop box might need
> to be visible .. but could this reside on a network server?

Each dropbox should be on the same machine as the synchronizer it is the
dropbox for. Replicas should never be visible directly.

> 3. This is a more fundamental question ... I am still not
> sure I understand why indirect syncs are important.  I
[quoted text clipped - 3 lines]
> minimize the problems that the self repairing properties
> of the farm correct?

Correct.

Signature

MichKa [MS]

This posting is provided "AS IS" with
no warranties, and confers no rights.

Vitalijus J. Karalius - 23 Sep 2003 17:43 GMT
JD-

The design master should not be in any regular synch schedule. Scheduling
synchs with the master as you describe it - is just asking for trouble -
evidenced by your result.

I would put farms on the clients also - the essence of farms is you have
other copies you can use in the event of damage or corruption (when....not
if), allowing clients to stay up and working even if temporarily
disconnected from the network. A single replica per client gives you no
cushion. Losing that replica forces you to fix it NOW. The price of disk
storage should make multiple copies (3+) a no brainer.

The basic reason for indirect synchs over a network is that hardware/user
problems can corrupt replicas doing direct synchs over the network.

> First I would like to that Michael Kaplan and Jack
> MacDonald for the information they have bestowed upon me
[quoted text clipped - 65 lines]
>
> JD
Jack MacDonald - 24 Sep 2003 05:56 GMT
>2. The local replicas on the client machines will not be
>visible to the farm or the rest of the network.  However,
>since the syncs will be initiated from the client machines
>is this necessary?  It seems that the drop box might need
>to be visible .. but could this reside on a network server?

In addition to Michael Kaplan's explanation, let me add this. I
initially sought to do the same thing -- put the dropboxes on the
server. I thought it would be "tidier" to have everything located
centrally. Technically, it *can* work, but it's the wrong thing to do.

Each synchronizer opens a file in the dropbox for the duration of the
time it is running. If the dropbox is on the local disk, that works
perfectly fine. But if the dropbox is on the server, and the LAN
connection goes down, then the synchronizer gets confused (I am not
sure of the exact process, but you can see the problem...)

Minimize the potential for problems by locating the dropbox on the
local disk of the synchronizer computer.

And yes, the dropbox must be visible, and the remote users must be
able to write into it.

=======================================================
Jack MacDonald
remove UPPERCASE LETTERS from email address              
Vancouver, B.C. Canada      
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www.geocities.com/jacksonmacd
 
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