Mailing-List: contact dev-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@couchdb.apache.org
Message-ID: <586277793.1250187074909.JavaMail.jira@brutus>
Date: Thu, 13 Aug 2009 11:11:14 -0700 (PDT)
From: "Robert Newson (JIRA)" <jira@apache.org>
To: dev@couchdb.apache.org
Subject: [jira] Commented: (COUCHDB-465) Produce sequential, but unique,
 document id's
In-Reply-To: <1495659442.1250179574899.JavaMail.jira@brutus>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/COUCHDB-465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12742911#action_12742911 ] 

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

Thanks!

Guessability is a concern, which means this might need to be switchable. Perhaps couch_seq_generator becomes couch_id_generator and an ini file chooses between the two strategies, defaulting to the safest, but worst-case, new_uuid behavior. To get good keys for b+tree insertion necessarily makes them more guessable as they'd have to be close to existing keys by design.

I do owe some quantitative benchmarking to support the assertions in the description. I did a 10k insertion test with a small document, {content: "hello"}, and average insertion rate per document was 2ms with random and 1ms with the patch. This was more to prove that I'd changed *something* rather than a measure of the actual improvement. I would expect to see improved insertion rates across a lot of scenarios, less difference between uncompacted and compacted size (barring document updates and deletes) as less of the b+tree is rewritten, and a smaller post-compaction size vs random. The exact extent of these improvements should be established by a decent benchmark. 


> 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: sequence_id.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.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.