OpenSearch/docs/reference/migration/migrate_2_0/crud.asciidoc

=== CRUD and routing changes

==== Explicit custom routing

Custom `routing` values can no longer be extracted from the document body, but
must be specified explicitly as part of the query string, or in the metadata
line in the <<docs-bulk,`bulk`>> API.  See <<migration-meta-fields>> for an
example.

==== Routing hash function

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 routing-related node settings have been deprecated:

`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.

==== Delete API with custom routing

The delete API used to be broadcast to all shards in the index which meant
that, when using custom routing, the `routing` parameter was optional. Now,
the delete request is forwarded only to the document holding the shard. If you
are using custom routing then you should specify the `routing` value when
deleting a document, just as is already required for the `index`, `create`,
and `update` APIs.

To make sure that you never forget a routing value, make routing required with
the following mapping:

[source,js]
---------------------------
PUT my_index
{
  "mappings": {
    "my_type": {
      "_routing": {
        "required": true
      }
    }
  }
}
---------------------------

==== All stored meta-fields returned by default

Previously, meta-fields like `_routing`, `_timestamp`, etc would only be
included in a GET request if specifically requested with the `fields`
parameter.  Now, all meta-fields which have stored values will be returned by
default.  Additionally, they are now returned at the top level (along with
`_index`, `_type`, and `_id`) instead of in the `fields` element.

For instance, the following request:

[source,sh]
---------------
GET /my_index/my_type/1
---------------

might return:

[source,js]
---------------
{
  "_index":     "my_index",
  "_type":      "my_type",
  "_id":        "1",
  "_timestamp": 10000000, <1>
  "_source": {
    "foo" : [ "bar" ]
  }
}
---------------
<1> The `_timestamp` is returned by default, and at the top level.


==== Async replication

The `replication` parameter has been removed from all CRUD operations
(`index`, `create`,  `update`, `delete`, `bulk`) as it interfered with the
<<indices-synced-flush,synced flush>> feature.  These operations are now
synchronous only and a request will only return once the changes have been
replicated to all active shards in the shard group.

Instead, use more client processes to send more requests in parallel.

==== Documents must be specified without a type wrapper

Previously, the document body could be wrapped in another object with the name
of the `type`:

[source,js]
--------------------------
PUT my_index/my_type/1
{
  "my_type": { <1>
    "text": "quick brown fox"
  }
}
--------------------------
<1> This `my_type` wrapper is not part of the document itself, but represents the document type.

This feature was deprecated before but could be reenabled with the
`mapping.allow_type_wrapper` index setting.  This setting is no longer
supported.  The above document should be indexed as follows:

[source,js]
--------------------------
PUT my_index/my_type/1
{
  "text": "quick brown fox"
}
--------------------------

==== Term Vectors API

Usage of `/_termvector` is deprecated in favor of `/_termvectors`.