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From "Bob Dionne (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-465) Produce sequential, but unique, document id's
Date Thu, 20 Aug 2009 11:27:15 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12745396#action_12745396
] 

Bob Dionne commented on COUCHDB-465:
------------------------------------

I tested this all against a clean checkout of trunk and it looks good. The new algorithm is
faster on inserts[1] but interestingly for single inserts is makes for a larger db pre-compact.
After compaction the db is smaller by a factor of 3 

I thought we leave the new "sequentially random" as the default? Paul, is the concern just
what's advertised to users? 

Algorithms based on the system clock I think can be problematic as they assume all machines
have the correct time. 


[1] http://gist.github.com/170982

> Produce sequential, but unique, document id's
> ---------------------------------------------
>
>                 Key: COUCHDB-465
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-465
>             Project: CouchDB
>          Issue Type: Improvement
>            Reporter: Robert Newson
>         Attachments: couch_uuids.patch, uuid_generator.patch
>
>
> Currently, if the client does not specify an id (POST'ing a single document or using
_bulk_docs) a random 16 byte value is created. This kind of key is particularly brutal on
b+tree updates and the append-only nature of couchdb files.
> Attached is a patch to change this to a two-part identifier. The first part is a random
12 byte value and the remainder is a counter. The random prefix is rerandomized when the counter
reaches its maximum. The rollover in the patch is at 16 million but can obviously be changed.
The upshot is that the b+tree is updated in a better fashion, which should lead to performance
benefits.

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