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Date: Mon, 5 Nov 2012 04:03:12 +0000 (UTC)
From: "Jens Alfke (JIRA)" <jira@apache.org>
To: dev@couchdb.apache.org
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Subject: [jira] [Commented] (COUCHDB-1259) Replication ID is not stable if
 local server has a dynamic port number
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    [ https://issues.apache.org/jira/browse/COUCHDB-1259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490441#comment-13490441 ] 

Jens Alfke commented on COUCHDB-1259:
-------------------------------------

> btw your example with couchbase mobile is generally solved by using the replication in pull mode only. So here it is relying on a fixed address to replicate.

*sigh* No, that is exactly the situation I was describing. The mobile client is the only one initiating replication; it pulls from the central (fixed-address) server, and pushes changes to it. So the mobile device's IP address and port are irrelevant, right? Except that the replication state document stored in _local has an ID based on several things _including_ the local server's address and port number. So the effect is that, every time the app launches, all the replication state gets lost/invalidated, and it has to start over again the next time it replicates.

TouchDB doesn't have this problem because I didn't write it with this design flaw :) Instead every local database has a UUID as suggested here, and that's used as part of the key.
                
> 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
>            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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