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From "Matt Goodall (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-529) Avoiding updating a doc's _rev if nothing changed
Date Thu, 15 Oct 2009 15:48:31 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12766103#action_12766103
] 

Matt Goodall commented on COUCHDB-529:
--------------------------------------

Relevant comments from the mailing list:

"the old revision of the document is part of the content used to generate the hash that becomes
the new revision.",  Adam Kocoloski.

"If you don't include the previous document's revision, then your hashes are unidirected and
don't form a Merkle tree.", Paul Davis.

So, it may not be possible without the overhead of re-calculating the old hash or something
similar.

> Avoiding updating a doc's _rev if nothing changed
> -------------------------------------------------
>
>                 Key: COUCHDB-529
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-529
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: Database Core
>            Reporter: Matt Goodall
>
> Would it be possible for CouchDB to use its deterministic rev algorithm to avoid writing
changes to the database if nothing has actually changed in the doc that is sent for update.
> The most obvious use case is the user who clicks an HTML form's submit button, instead
of using the back button, when they haven't changed anything. I suspect most applications
do not check if the user made any changes and therefore end up sending exactly the same data
back as an update ... unnecessarily creating a new document rev, growing the database, invalidating
views, triggering _changes updates, etc.
> If CouchDB could determine that the new document is the same as the old document then
it could avoid writing to disc and return the current _rev in the response.

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