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https://issues.apache.org/jira/browse/COUCHDB-1259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13089976#comment-13089976
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Jens Alfke commented on COUCHDB-1259:
-------------------------------------
@Jason: The reason I filed this bug report is that the URL of a database in
Couchbase Mobile *isn't* unique. It's barely meaningful at all; it's of the
form "http://127.0.0.1:nnnnn"; where "nnnnn" is an upredictable port number
assigned by the TCP stack at launch time. That URL isn't even exposed to the
outside world because the CouchDB server is only listening on the loopback
interface.
The state that's being represented by a replication ID is the contents of the
database (at least as it was when it last synced.) So it seems the ID should be
something that sticks to the database itself, not to any ephemeral
manifestation like a URL.
> Replication ID is not stable if local server has a dynamic port number
> ----------------------------------------------------------------------
>
> Key: COUCHDB-1259
> URL: https://issues.apache.org/jira/browse/COUCHDB-1259
> Project: CouchDB
> Issue Type: Bug
> Components: Replication
> Affects Versions: 1.1
> Reporter: Jens Alfke
>
> 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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