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