This PR adds per-field metadata that can be set in the mappings and is later
returned by the field capabilities API. This metadata is completely opaque to
Elasticsearch but may be used by tools that index data in Elasticsearch to
communicate metadata about fields with tools that then search this data. A
typical example that has been requested in the past is the ability to attach
a unit to a numeric field.
In order to not bloat the cluster state, Elasticsearch requires that this
metadata be small:
- keys can't be longer than 20 chars,
- values can only be numbers or strings of no more than 50 chars - no inner
arrays or objects,
- the metadata can't have more than 5 keys in total.
Given that metadata is opaque to Elasticsearch, field capabilities don't try to
do anything smart when merging metadata about multiple indices, the union of
all field metadatas is returned.
Here is how the meta might look like in mappings:
```json
{
"properties": {
"latency": {
"type": "long",
"meta": {
"unit": "ms"
}
}
}
}
```
And then in the field capabilities response:
```json
{
"latency": {
"long": {
"searchable": true,
"aggreggatable": true,
"meta": {
"unit": [ "ms" ]
}
}
}
}
```
When there are no conflicts, values are arrays of size 1, but when there are
conflicts, Elasticsearch includes all unique values in this array, without
giving ways to know which index has which metadata value:
```json
{
"latency": {
"long": {
"searchable": true,
"aggreggatable": true,
"meta": {
"unit": [ "ms", "ns" ]
}
}
}
}
```
Closes#33267
Several files in the REST APIs nav section are included using
:leveloffset: tags. This increments headings (h2 -> h3, h3 -> h4, etc.)
in those files and removes the :leveloffset: tags.
Other supporting changes:
* Alphabetizes top-level REST API nav items.
* Change 'indices APIs' heading to 'index APIs.'
* Changes 'Snapshot lifecycle management' heading to sentence case.
Today the `_field_caps` API returns the list of indices where a field
is present only if this field has different types within the requested indices.
However if the request is an index pattern (or an alias, or both...) there
is no way to infer the indices if the response contains only fields that have
the same type in all indices. This commit changes the response to always return
the list of indices in the response. It also adds a way to retrieve unmapped field
in a specific section per field called `unmapped`. This section is created for each field
that is present in some indices but not all if the parameter `include_unmapped` is set to
true in the request (defaults to false).
This change introduces a new API called `_field_caps` that allows to retrieve the capabilities of specific fields.
Example:
````
GET t,s,v,w/_field_caps?fields=field1,field2
````
... returns:
````
{
"fields": {
"field1": {
"string": {
"searchable": true,
"aggregatable": true
}
},
"field2": {
"keyword": {
"searchable": false,
"aggregatable": true,
"non_searchable_indices": ["t"]
"indices": ["t", "s"]
},
"long": {
"searchable": true,
"aggregatable": false,
"non_aggregatable_indices": ["v"]
"indices": ["v", "w"]
}
}
}
}
````
In this example `field1` have the same type `text` across the requested indices `t`, `s`, `v`, `w`.
Conversely `field2` is defined with two conflicting types `keyword` and `long`.
Note that `_field_caps` does not treat this case as an error but rather return the list of unique types seen for this field.
Adrien Grand
István Zoltán Szabó
James Rodewig
Julie Tibshirani
Jim Ferenczi
Darren Meiss
Clinton Gormley
Jim Ferenczi