.. Licensed under the Apache License, Version 2.0 (the "License"); you may not
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..   http://www.apache.org/licenses/LICENSE-2.0
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.. distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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.. _release/2.0.x:

============
2.0.x Branch
============

.. contents::
    :depth: 1
    :local:

.. _release/2.0.0:

Version 2.0.0
=============

* Native clustering is now supported. Rather than use CouchDB replication
  between multiple, distinct CouchDB servers, configure a cluster of CouchDB
  nodes. These nodes will use an optimized Erlang-driven 'internal replication'
  to ensure data durability and accessibility. Combine a clustered CouchDB with
  a load balancer (such as ``haproxy``) to scale CouchDB out horizontally. More
  details of the clustering feature are available in the :ref:`cluster`.
* `Futon` replaced by brand-new, completely re-engineered `Fauxton` interface.
  URL remains the same.
* The new Mango Query Server provides a simple JSON-based way to perform CouchDB
  queries without JavaScript or MapReduce. Mango Queries have a similar indexing
  speed advantage over JavaScript Queries than the Erlang Queries have (2x-10x
  faster indexing depending on doc size and system configuration). We recommend
  all new apps start using Mango as a default. Further details are available
  in the :ref:`_find, _index and _explain API <api/db/_find>`.
* Mango :ref:`selectors <changes/filter/selector>` can be used in _changes
  feeds instead of JavaScript MapReduce filters. Mango has been tested to be
  up to an order of magnitude (10x) faster than JavaScript in this application.
* :ref:`Rewrite rules <api/ddoc/rewrite>` for URLs can be performed using
  JavaScript functions.
* :ref:`Multiple queries <api/ddoc/view/multiple_queries>` can be made of a
  view with a single HTTP request.
* Views can be queried with sorting turned off ( ``sorted=false``) for a
  performance boost.
* The global changes feed has been enhanced. It is now resumable and persistent.
* New endpoints added (documentation forthcoming):

  * :ref:`api/server/membership` shows all nodes in a cluster
  * ``/_bulk_get`` speeds up the replication protocol over low-latency
    connections
  * ``/_node/`` api to access individual nodes' configuration and compaction
    features
  * ``/_cluster_setup`` api to set up a cluster from scratch.
  * ``/_up`` api to signal health of a node to a load-balancer
  * ``/db/_local_docs`` and ``/db/_design_docs`` (similar to ``/db/_all_docs``)

* The ``/_log`` endpoint was removed.
* "Backend" interface on port 5986 used for specific cluster admin tasks. Of
  interest are the ``_nodes`` and ``_dbs`` databases visible only through this
  interface.
* Support added for Erlang/OTP 17.x, 18.x and 19
* New streamlined build system written for Unix-like systems and Microsoft
  Windows
* :ref:`Configuration <api/config>` has moved from ``/_config`` to
  ``/_node/{node-name}/_config``
* ``instance_start_time`` now always reports ``"0"``.

.. _release/2.0.x/upgrade:

Upgrade Notes
=============

* The update sequences returned by the :ref:`api/db/changes` feed are no longer
  integers. They can be any JSON value. Applications should treat them as opaque
  values and return them to CouchDB as-is.
* Temporary views are no longer supported.
* It is possible to have multiple replicator databases.
  ``replicator/db`` config option has been removed.
  Instead ``_replicator`` and any database names ending
  with the ``/_replicator`` suffix will be recognized as
  replicator databases by the system.
* Note that the semantics of some API calls have changed due to the introduction
  of the clustering feature. Specifically, make note of the difference between
  receiving a ``201`` and a ``202`` when storing a document.
* ``all_or_nothing`` is no longer supported by the :ref:`bulk_docs
  <api/db/bulk_docs>` API
* After updating a design document containing a ``show``, an immediate GET to
  that same ``show`` function may still return results from the previous
  definition. This is due to design document caching, which may take a few
  seconds to fully evict, or longer (up to ~30s) for a clustered installation.

.. _release/2.0.x/knownissues:

Known Issues
============

All `known issues`_ filed against the 2.0 release are contained within the
official `CouchDB JIRA instance` or `CouchDB GitHub Issues`.

The following are some highlights of known issues for which fixes did not land
in time for the 2.0.0 release:

* :issue:`2980`: The replicator (whether invoked via ``_replicate`` or a
  document stored in the ``_replicator`` database) understands two kinds of
  source and target:

  #. A URL (e.g., ``https://foo:bar@foo.com/db1``), called a "remote" source or
     target
  #. A database name (e.g., ``db1``), called a "local" source or target.

  Whenever the latter type is used, this refers to a local unclustered
  database, not a clustered one.

  In a future release we hope to support "local" source or target specs to
  clustered databases. For now, we recommend always using the URL format for
  both source and target specifications.
* :issue:`3034`: CouchDB will occasionally return 500 errors when multiple
  clients attempt to PUT or DELETE the same database concurrently.
* :issue:`3119`: Adding nodes to a cluster fails if the Erlang node name
  is not ``couchdb`` (of the form ``couchdb@hostname``.)
* :issue:`3050`: Occasionally the ``dev/run`` script used for development
  purposes to start a local 3-node cluster will fail to start one or more
  nodes.
* :issue:`2817`: The compaction daemon will only compact views for shards
  that contain the design document.
* :issue:`2804`: The fast_view optimization is not enabled on the clustered
  interface.
* :ghissue:`656`: The OAuth 1.0 support is broken and deprecated. It will be
  removed in a future version of CouchDB.

.. _known issues: https://s.apache.org/couchdb-2.0-known-issues
.. _CouchDB JIRA instance: https://issues.apache.org/jira/browse/COUCHDB
.. _CouchDB GitHub Issues: https://github.com/apache/couchdb/issues