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From "Benoit Chesneau (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-1259) Replication ID is not stable if local server has a dynamic port number
Date Mon, 05 Nov 2012 03:18:13 GMT


Benoit Chesneau commented on COUCHDB-1259:

I don't. The replication is fundamentally a peer to peer protocol. or master to master. whatever.

It is and should be expected that a node can disappear for many reasons. Relying on a server
id is one of the  possibilities to restart automatically a replication, other would use other
parameters based on the ip and the location, etc... It is the responsibility of the application
to know that. As a protocol the replication shouldn't force this way imo. As a client the
replicator shouldn't too. It is already doing the best effort imo: ie restarting for the same
ip, port and properties of the replication. 

As a side note, this is one of the reason the 0 port could be used here instead of letting
your *application* fix a port. 0 won't change. And you could rely with the *application* on
a unique property in the replication properties.
> Replication ID is not stable if local server has a dynamic port number
> ----------------------------------------------------------------------
>                 Key: COUCHDB-1259
>                 URL:
>             Project: CouchDB
>          Issue Type: Bug
>          Components: Replication
>    Affects Versions: 1.1
>            Reporter: Jens Alfke
>            Assignee: Robert Newson
>            Priority: Blocker
>             Fix For: 1.3
>         Attachments: couchdb-1259.patch, couchdb-1259.patch
> I noticed that when Couchbase Mobile running on iOS replicates to/from a remote server
(on iriscouch in this case), the replication has to fetch the full _changes feed every time
it starts. Filipe helped me track down the problem -- the replication ID is coming out different
every time. The reason for this is that the local port number, which is one of the inputs
to the hash that generates the replication ID, is randomly assigned by the OS. (I.e. it uses
a port number of 0 when opening its listener socket.) This is because there could be multiple
apps using Couchbase Mobile running on the same device and we can't have their ports colliding.
> The underlying problem is that CouchDB is attempting to generate a unique ID for a particular
pair of {source, destination} databases, but it's basing it on attributes that aren't fundamental
to the database and can change, like the hostname or port number.
> One solution, proposed by Filipe and me, is to assign each database (or each server?)
a random UUID when it's created, and use that to generate replication IDs.
> Another solution, proposed by Damien, is to have CouchDB let the client work out the
replication ID on its own, and set it as a property in the replication document (or the JSON
body of a _replicate request.) This is even more flexible and will handle tricky scenarios
like full P2P replication where there may be no low-level way to uniquely identify the remote
database being synced with.

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