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From J Chris Anderson <jch...@gmail.com>
Subject Re: Preserving seq order through replication
Date Fri, 05 Mar 2010 16:56:29 GMT

On Mar 5, 2010, at 8:08 AM, Dirkjan Ochtman wrote:

> Hi there,
> 
> I recently started using continuous replication to propagate a
> document stream from a producing server to a consuming server. The
> producing server is fed by a single process that puts messages in, and
> on the consuming server we have a process reading the continuous
> changes feed to get messages back out and process them. We migrated to
> this from having a single server that both processes talked to because
> the connection between the servers isn't always reliable,
> unfortunately.
> 
> This worked rather well for about 50 hours, but now it turns out that
> in some cases the continuous replication doesn't always preserve the
> ordering of the sequence. That is, the insertion order, which is
> consistent on the producing server (as expected, as there's a single
> feeding process doing a single update per document) doesn't match the
> order in the continuous feed of changes on the consuming server.
> 
> This is kind of a WTF. Could it be fixed?

I don't think this is a bug. Preserving order across replicas is definitely something that
won't scale across a cluster (especially if it is partitioned), so we wouldn't want to attempt
guarantees like that at smaller scales.

Of course, if you have a field you'd like to order operations on, you can mark your documents
with it and use view queries to drive the asynchronous processing.

Chris

> 
> Cheers,
> 
> Dirkjan


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