[[breaking-changes-1.4]]
== Breaking changes in 1.4

This section discusses the changes that you need to be aware of when migrating
your application from Elasticsearch 1.x to Elasticsearch 1.4.

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=== Percolator

In indices created with version `1.4.0` or later, percolation queries can only
refer to fields that already exist in the mappings in that index. There are
two ways to make sure that a field mapping exist:

* Add or update a mapping via the <<indices-create-index,create index>> or
  <<indices-put-mapping,put mapping>> apis.
* Percolate a document before registering a query. Percolating a document can
  add field mappings dynamically, in the same way as happens when indexing a
  document.

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=== Aliases

<<indices-aliases,Aliases>> can include <<query-dsl,filters>> which
are automatically applied to any search performed via the alias.
<<filtered,Filtered aliases>> created with version `1.4.0` or later can only
refer to field names which exist in the mappings of the index (or indices)
pointed to by the alias.

Add or update a mapping via the <<indices-create-index,create index>> or
<<indices-put-mapping,put mapping>> apis.

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=== Indices APIs

The get warmer api will return a section for `warmers` even if there are
no warmers.  This ensures that the following two examples are equivalent:

[source,js]
--------------------------------------------------
curl -XGET 'http://localhost:9200/_all/_warmers'

curl -XGET 'http://localhost:9200/_warmers'
--------------------------------------------------

The <<alias-retrieving, get alias api>> will return a section for `aliases` even if there are
no aliases.  This ensures that the following two examples are equivalent:

[source,js]
--------------------------------------------------
curl -XGET 'http://localhost:9200/_all/_aliases'

curl -XGET 'http://localhost:9200/_aliases'
--------------------------------------------------

The <<indices-get-mapping, get mapping api>> will return a section for `mappings` even if there are
no mappings.  This ensures that the following two examples are equivalent:

[source,js]
--------------------------------------------------
curl -XGET 'http://localhost:9200/_all/_mappings'

curl -XGET 'http://localhost:9200/_mappings'
--------------------------------------------------

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=== Bulk UDP

Bulk UDP has been deprecated and will be removed in 2.0.
You should use <<docs-bulk,the standard bulk API>> instead.
Each cluster must have an elected master node in order to be fully operational. Once a node loses its elected master
node it will reject some or all operations.

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=== Zen discovery

On versions before `1.4.0.Beta1` all operations are rejected when a node loses its elected master. From `1.4.0.Beta1`
only write operations will be rejected by default. Read operations will still be served based on the information available
to the node, which may result in being partial and possibly also stale. If the default is undesired then the
pre `1.4.0.Beta1` behaviour can be enabled, see: <<modules-discovery-zen,no-master-block>>

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=== More Like This Field

The More Like This Field query has been deprecated in favor of the <<query-dsl-mlt-query, More Like This Query>>
restrained set to a specific `field`. It will be removed in 2.0.

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=== MVEL is deprecated

Groovy is the new default scripting language in Elasticsearch, and is enabled in `sandbox` mode
by default.  MVEL has been removed from core, but is available as a plugin:
https://github.com/elastic/elasticsearch-lang-mvel