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Whats the exact algorithm to calculate the CouchDB revision number. CouchDB uses a deterministic algorithm to calculate the document revision number. Here is one relevant doc I found: https://stackoverflow.com/questions/5954864/how-does-couchdb-calculate-the-revision-number

Buts its all in elrang, I am trying to implement it in dart. I use sample document : {"_id":"123-this-is-an-id","hello":"world","testing":123} for testing.

When I do the MD5 hash of it , its gives me : f0853833850bce08dce0896e010a375e, where as the couchdb revision number is : 

"_rev": "1-43dce8fe7e9a26b49390e3727a015cc0"

I google it everywhere, but if I can find the algorithm some where in text , UI can convert it into dart.

gdelfino
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user3769778
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2 Answers2

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The algorithm is Erlang-specific as it involves the Erlang External Term Format. (CouchDB is written in Erlang.) It would be hard to re-implement in a different language.

It is indeed an MD5 hash, of a binary term representation of the document and its attributes.

I am unsure if the code can be reproduced, so you can find it in the couchdb repository. Note that for the main branch, the new_revid function moved to the Fabric DB implementation.

PouchDB has an entirely different hashing algorithm - its revs are MD5 hashes of the JSON representation of the document without its revision field.

So as you can see, it is not critical to reproduce the algorithm perfectly - you will only run into conflicts when syncing two databases on different platforms that both create docs. And even then, the conflict resolution algorithm should take care of it.

Leonid Shevtsov
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So after some time, I got to know that couchdb calculates revision number as such:

seq_num-md5HashOfDocJsonContentWithoutRevField
user3769778
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