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From "Paul Joseph Davis (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-1373) Time-order​ed document ids including the database identity
Date Sat, 31 Dec 2011 23:21:30 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-1373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13178095#comment-13178095
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Paul Joseph Davis commented on COUCHDB-1373:
--------------------------------------------

Your whitespace is wonky. Indentation in Erlang code should be four spaces and not tabs. There's
also some pure white-space changes.

Also, you should add a note in the default.ini.tpl.in file to indicate that the new algorithm
exists as well as the fact that it requires the couchdb/machine_id setting to do what it's
supposed to. I'm also hesitating if machine_id shouldn't be in the uuid section or not. Not
super important but I find it a bit odd to have it there.

Also, I wonder if it'd be possible to generate some sort of default machine id if one isn't
specified. Something like, a sha of all mac addresses in sorted order? Then again I'm not
sure how hard it'd be to get that list from Erlang in a portable fashion.
                
> Time-order​ed document ids including the database identity
> ----------------------------------------------------------
>
>                 Key: COUCHDB-1373
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-1373
>             Project: CouchDB
>          Issue Type: Improvement
>          Components: Database Core
>            Reporter: Nick North
>            Priority: Minor
>              Labels: uuid
>         Attachments: couch_uuids.patch
>
>
> This suggestion is for an enhancement to the document id generation algorithms in CouchDb.
I am new to CouchDb, and this question addresses an old issue (https://issues.apache.org/jira/browse/COUCHDB-465)
so please forgive me if I am retreading old ground.
> My application has a number of mutually replicating CouchDb instances and I would like
document ids to be monotonically-increasing per-instance, and globally unique, and for the
instance where the document was created to be determinable from the id. (To be more accurate
- I don't need to know anything about the instance itself; just whether any two documents
originated from the same instance.) The utc_random algorithm is not far from meeting these
requirements, as ids are monotonic and almost certainly globally unique. However, the instance
cannot be determined from the id, and there is a tiny chance of an id clash between two instances.
Both of these issues could be solved if the random part of the id could be replaced with a
suffix that is fixed in the ini file for each instance.
> To address this I have a modified version of couch_uuids.erl introducing a new utc_machine_id
algorithm which reads a machine_id string from the ini file and then generates ids using an
internal utc_suffix method that just appends the string to the usual utc 14-byte string. utc_random
then also uses the utc_suffix method, but its suffix is the usual random byte string.
> However, it is obviously a nuisance to have to maintain a non-standard distribution,
so I wondered if there is enough call for this sort of thing to make it a part of the standard
distribution? If there is, I'd be very happy to make my code available for discussion/modification/inclusion.
If there are good reasons why this is a bad idea, then I'd also be very interested to hear
them so that I can rethink my ideas. (It happens that the privacy and guessability concerns
raised in the original discussion do not apply in my case.) If this question has been beaten
to death, then I'm sorry for bothering the group, and would be grateful if someone could point
me to the discussions so that I can understand the issues.

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