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From "Robert Newson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-465) Produce sequential, but unique, document id's
Date Thu, 20 Aug 2009 11:43:14 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12745403#action_12745403
] 

Robert Newson commented on COUCHDB-465:
---------------------------------------


I just noticed that Paul's implementation is not as Brian described; the suffix is always
random with no guarantee the id N+1 is strictly higher than id N;

+    list_to_binary(Prefix ++ couch_util:to_hex(crypto:rand_bytes(9))).

In practise it just means that id's generated in the same millisecond are randomly ordered.
Does that matter?

> 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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