OpenSearch/docs/reference/migration/migrate_2_1.asciidoc

[[breaking-changes-2.1]]
== Breaking changes in 2.1

This section discusses the changes that you need to be aware of when migrating
your application to Elasticsearch 2.1.

* <<breaking_21_search_changes>>
* <<breaking_21_update_changes>>
* <<breaking_21_removed_features>>
* <<breaking_21_more_like_this>>
* <<breaking_21_nested_sorting>>
* <<breaking_21_index_apis>>

[[breaking_21_search_changes]]
=== Search changes

==== `search_type=scan` deprecated

The `scan` search type has been deprecated. All benefits from this search
type can now be achieved by doing a scroll request that sorts documents in
`_doc` order, for instance:

[source,sh]
---------------
GET /my_index/_search?scroll=2m
{
  "sort": [
    "_doc"
  ]
}
---------------

Scroll requests sorted by `_doc` have been optimized to more efficiently resume
from where the previous request stopped, so this will have the same performance
characteristics as the former `scan` search type.

==== from + size limits

Elasticsearch will now return an error message if a query's `from` + `size` is
more than the `index.max_result_window` parameter. This parameter defaults to
10,000 which is safe for almost all clusters. Values higher than can consume
significant chunks of heap memory per search and per shard executing the
search. It's safest to leave this value as it is an use the scroll api for any
deep scrolling but this setting is dynamic so it can raised or lowered as
needed.

[[breaking_21_update_changes]]
=== Update changes

==== Updates now `detect_noop` by default

We've switched the default value of the `detect_noop` option from `false` to
`true`. This means that Elasticsearch will ignore updates that don't change
source unless you explicitly set `"detect_noop": false`. `detect_noop` was
always computationally cheap compared to the expense of the update which can be
thought of as a delete operation followed by an index operation.

[[breaking_21_removed_features]]
=== Removed features

==== `indices.fielddata.cache.expire`

The experimental feature `indices.fielddata.cache.expire` has been removed.
For indices that have this setting configured, this config will be ignored.

[[breaking_21_more_like_this]]
=== More Like This

The MoreLikeThisQueryBuilder#ignoreLike methods have been deprecated in favor
of using the unlike methods.

MoreLikeThisBuilder#addItem has been deprecated in favor of using
MoreLikeThisBuilder#addLikeItem.

[[breaking_21_nested_sorting]]
=== Nested sorting

If sorting on field inside a nested object then the `nested_path` should be specified.
Before there was an attempt to resolve the nested path automatically, but that was sometimes incorrect.
To avoid confusion the `nested_path` should always be specified.

[[breaking_21_index_apis]]
=== Index APIs

==== Optimize API

The Optimize API has been deprecated, all new optimize actions should use the new Force Merge API.