OpenSearch/docs/reference/migration/migrate_2_0.asciidoc

[[breaking-changes-2.0]]
== Breaking changes in 2.0

This section discusses the changes that you need to be aware of when migrating
your application to Elasticsearch 2.0.

=== Indices API

The <<alias-retrieving, get alias api>> will, by default produce an error response 
if a requested index does not exist. This change brings the defaults for this API in 
line with the other Indices APIs. The <<multi-index>> options can be used on a request 
to change this behavior

`GetIndexRequest.features()` now returns an array of Feature Enums instrad of an array of String values.
The following deprecated methods have been removed:
* `GetIndexRequest.addFeatures(String[])` - Please use `GetIndexRequest.addFeatures(Feature[])` instead
* `GetIndexRequest.features(String[])` - Please use `GetIndexRequest.features(Feature[])` instead
* `GetIndexRequestBuilder.addFeatures(String[])` - Please use `GetIndexRequestBuilder.addFeatures(Feature[])` instead
* `GetIndexRequestBuilder.setFeatures(String[])` - Please use `GetIndexRequestBuilder.setFeatures(Feature[])` instead

=== Partial fields

Partial fields were deprecated since 1.0.0beta1 in favor of <<search-request-source-filtering,source filtering>>.

=== More Like This Field

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

=== Routing

The default hash function that is used for routing has been changed from djb2 to
murmur3. This change should be transparent unless you relied on very specific
properties of djb2. This will help ensure a better balance of the document counts
between shards.

In addition, the following node settings related to routing have been deprecated:

[horizontal]

`cluster.routing.operation.hash.type`::

  This was an undocumented setting that allowed to configure which hash function
  to use for routing. `murmur3` is now enforced on new indices.

`cluster.routing.operation.use_type`::

  This was an undocumented setting that allowed to take the `_type` of the
  document into account when computing its shard (default: `false`). `false` is
  now enforced on new indices.

=== Store

The `memory` / `ram` store (`index.store.type`) option was removed in Elasticsearch 2.0.

=== Term Vectors API

Usage of `/_termvector` is deprecated, and replaced in favor of `/_termvectors`.

=== Script fields

Script fields in 1.x were only returned as a single value. So even if the return
value of a script used to be list, it would be returned as an array containing
a single value that is a list too, such as:

[source,json]
---------------
"fields": {
  "my_field": [
    [
      "v1",
      "v2"
    ]
  ]
}
---------------

In elasticsearch 2.x, scripts that return a list of values are considered as
multivalued fields. So the same example would return the following response,
with values in a single array.

[source,json]
---------------
"fields": {
  "my_field": [
    "v1",
    "v2"
  ]
}
---------------

=== Java API

Some query builders have been removed or renamed:

* `commonTerms(...)` renamed with `commonTermsQuery(...)`
* `queryString(...)` renamed with `queryStringQuery(...)`
* `simpleQueryString(...)` renamed with `simpleQueryStringQuery(...)`
* `textPhrase(...)` removed
* `textPhrasePrefix(...)` removed
* `textPhrasePrefixQuery(...)` removed
* `filtered(...)` removed. Use `filteredQuery(...)` instead.
* `inQuery(...)` removed.

=== Terms filter lookup caching

The terms filter lookup mechanism does not support the `cache` option anymore
and relies on the filesystem cache instead. If the lookup index is not too
large, it is recommended to make it replicated to all nodes by setting
`index.auto_expand_replicas: 0-all` in order to remove the network overhead as
well.