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From Adam Kocoloski <>
Subject Re: CouchDB: 2.0 & 1.6.1 database compatibility
Date Fri, 07 Oct 2016 13:43:42 GMT
Lots of good questions there.

On the storage size, note that even when you write only one revision of each document the
database will accumulate some wasted space. Inserts to the database cause internal btree structures
to be updated, and due to the copy-on-write nature of the storage engine the old btree nodes
are left around in the file.

We did make some changes in the compaction system that produce smaller files at the end of
the day. You can read more about those changes here -
<> - but they don’t explain
the difference that you reported. Perhaps you didn’t compact the source database at all?

You are correct that both design documents and mango will build btree-based indexes to answer
their queries. I would like to see us add functionality to mango over time so that it can
cover the large majority of use cases where folks need to appeal to views in design documents,
but we’re not quite there yet. One example where mango cannot help you today is reduce functions;
if you want to aggregate the values in your index you need to drop down and build a view for

In terms of performance, mango should be moderately faster at building an index because there’s
no JavaScript roundtrip. Querying performance should be ~identical. Cheers,


> On Oct 7, 2016, at 7:56 AM, Thanos Vassilakis <> wrote:
> Good questions 
> Sent from my iPhone
>> On Oct 7, 2016, at 5:29 AM, Bogdan Andu <> wrote:
>> I see the data management is totally different(and better).
>> now there is a _dbs.couch for a registry-like database for databases
>> and actual databases are located in data/shards subdirectories.
>> so.. only replication works here..
>> and one can replicate many databases in parallel.
>> another difference I see is the size of databases.
>> 2.0 version keep a very small size of databases compared to 1.6.1 version.
>> Is there any change in storage engine that makes so big differences in
>> database sizes?
>> all records in db1 in 1.6.1 have only one revision like (1-...) format
>> db1 in 1.6.1 is 2.5GB with 362849 records
>> after replication:
>> db1 in 2.0 has 69.3 MB with 362849 records
>> when is recommended to use design documents and when mango queries.
>> is mango intended to replace design documents although I assume both
>> build a view tree for the query in question.
>> which one is faster?
>> what are the use-cases for each one of the query methods?
>> Thanks,
>> Bogdan
>>> On Fri, Oct 7, 2016 at 11:20 AM, max <> wrote:
>>> Hi,
>>> Install 2.0 version on another server or just make it listen on different
>>> port than 1.6 then replicate your data ;)
>>> 2016-10-07 9:49 GMT+02:00 Bogdan Andu <>:
>>>> Hello,
>>>> I configured a single-node CouchDB 2.0 instance and
>>>> I copied in data directory 1.6.1 couch databases.
>>>> But the databases does not show up in Fauxton, only the
>>>> test databases:
>>>> ["_global_changes","_replicator","_users","verifytestdb"].
>>>> Is there a way to make CouchDB 2.0 read 1.6.1 couch files
>>>> without importing?
>>>> /Bogdan

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