Mirroring /Replication

Mirroring /Replication

by Jan Willem Smeenk -
Number of replies: 6

I’m the IT manager of the International school of Tanganyika (Tanzania) and we are looking into implementing Moodle
One of the biggest problems we are facing here in Tanzania is connectivity related. There are about 6 ISP’s here in Tanzania each connected via Satellite to the rest of the Internet. We have our own Satellite link.So if a home user wants to reach a server in School traffic will travel a Satellite hop twice. 

Hosting the Moodle server on the school network would make access from outside very slow. Hosting it outside school would make access from the school network very slow.

My question is now:

Could we setup a Moodle on two mirrored servers?

Ideally we would have a Master server in school and a Slave server hosted somewhere overseas. Updates in the Master server should be replicated after school hours (or overnight) to the slave server. Updates on the slave server should be replicated directly to the master server. In that way we would use our Internet bandwidth most efficiently. (See graph attached to get an idea of our Internet bandwith usage)

Any thoughts?

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In reply to Jan Willem Smeenk

Re: Mirroring /Replication

by Visvanath Ratnaweera -
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I can't think of a satisfactory solution to your problem, unless you declare the slave read-only!

The point is that the additional information depend on what is available at the time of adding that piece of information. Allowing a Moodle instance to grow in _two_ places and then merging does not make sense.

I know this problem of two local ISPs only talking to each other only through overseas lines. They have to put up a peer exchange point!
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In reply to Jan Willem Smeenk

Re: Mirroring /Replication

by Eric Malone -
Ahh, good 'ole satellite internet. I remember a friend of mine who lived out in the middle of nowhere got this, it had pro's and con's.... great download bandwidth.... horrible latency speed.

Have you considered getting a dial-up line? I know you said that all the ISP's were satellite, but surely there is a dial-up provider? If so, you could bond two or three connections and have a quick, though bandwidth-limited, connection. You could also provide dial-up access yourself to the moodle site... if the infastructure exists.

Have you considered wireless? If you have a cell phone that works where you are, you may be able to do some sort of mobile wireless connection.

Have you considered praying for WiMAX? If and when implemented, it will provide the world with internet access with access points that send out a signal 20+ miles.


I may have the wrong idea of your conditions in Tanzania... are there any non-satellite options?
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In reply to Jan Willem Smeenk

Re: Mirroring /Replication

by Cornel van Lingen -

As far as I can see, the problem with replicating moodle is the auto increment IDs. For general activity tables this is not a problem, but when these IDs are used for referencial integrity, then you have a problem.

You can logically replicate activities, logs, grades etc. from remote sites to a central site, but only one site can be allowed for admin to courses and users, because of the referencial integrity. This is an opinion we have open under another database forum, just search for replication.

We have developed a utility that does replication of this nature between 68 remote sites and one mother moodle. Like I say in the other forum, a moodle expert would have to give us a good opinion and then we can make this available to everyone. It is quite risky and you can really mess things up.

So lets ask enough people and hopefully someone like Martin can give us a solid opinion.

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In reply to Cornel van Lingen

Re: Mirroring /Replication

by harshal mundiwale -

Can you share something about this utility or the way it written to handle the database replication especially the auto increment IDs?

Thanks

--Harshal

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