Simple CouchDB multi-master clustering via Nginx

http://ephemera.karmi.cz/post/247255194/simple-couchdb-multi-master-clustering-via-nginx

by va_coder • 17 years ago

39 8 17 years ago

ephemera.karmi.cz

I totally agree with the sentiment of the post - using CouchDB has simply been unbelievable amounts of fun (and certain types of applications would be painful if not impossible to design without it).

The existence of projects like couchdb-python and couchdb-lucene are just icing on a very tasty cake.

kolosy• 17 years ago

seconded. it's interesting how it forces you to build for scale right away.

z80002• 17 years ago

I'm not too familiar with multi master replication. What happens when a request handled by server A is followed by a subsequent request that is routed to server B before server A has replicated the changes from the first request? The client would expect a certain state on the "server" given the first request but it certainly seems possible to invalidate that.

jdminhbg• 17 years ago

If you attempt to update a record, you send a uuid to server B representing the document you're attempting to update; if sever B doesn't have that document yet (either because it hasn't been created on server B or because it is not yet updated to the latest changes on server B), that change will be rejected.

If you are just expecting the document to be a member of a list (say, you put an order on server A, then look for all orders belonging to a customer on server B), you're not guaranteed to see it. This is 'eventual consistency' -- in practice, you want to be sure that you can live with this as a tradeoff.

z80002• 17 years ago

Thank you.

smwhreyebelong• 17 years ago

The google tech talk on CouchDB talks about this problem :

http://www.youtube.com/watch?v=ESDBM9-U804

54:14 in, someone asks a similar question

mark_l_watson2• 17 years ago

Great writeup. I use CouchDB behind nginx anyway for simple authentication so I'll have to try this. The only problem is "continuous replication currently does not survive server restart" - that is not so good.

mark_l_watson2• 17 years ago

OK, apparently this is not such a problem; from the book: "At the time of writing, CouchDB doesn’t remember continuous replications over a server restart. For the time being, you are required to trigger them again, when you restart CouchDB."

So, put something in /etc/rc.local for each server to start the replication again.

Simple CouchDB multi-master clustering via Nginx

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