Add documentation for the new parent-join field (#25227)

* Add documentation for the new parent-join field

This commit adds the docs for the new parent-join field.
It explains how to define, index and query this new field.

Relates #20257
This commit is contained in:
Jim Ferenczi 2017-06-16 11:13:23 +02:00 committed by GitHub
parent ff9edb627e
commit ccb3c9aae7
3 changed files with 499 additions and 55 deletions

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@ -38,6 +38,8 @@ string:: <<text,`text`>> and <<keyword,`keyword`>>
<<percolator>>:: Accepts queries from the query-dsl
<<parent-join>>:: Defines parent/child relation for documents within the same index
[float]
=== Multi-fields
@ -84,7 +86,7 @@ include::types/token-count.asciidoc[]
include::types/percolator.asciidoc[]
include::types/parent-join.asciidoc[]

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@ -0,0 +1,417 @@
[[mapping-parent-join-field]]
=== `join` datatype
The `join` datatype is a special field that creates
parent/child relation within documents of the same index.
This `relations` section defines a set of possible relations within the documents,
each relation being a parent name and a child name.
A parent/child relation can be defined as follows:
[source,js]
--------------------------------------------------
PUT my_index
{
"mappings": {
"doc": {
"properties": {
"my_join_field": { <1>
"type": "join",
"relations": {
"my_parent": "my_child" <2>
}
}
}
}
}
}
--------------------------------------------------
// CONSOLE
<1> The name for the field
<2> Defines a single relation where `my_parent` is parent of `my_child`.
To index a document with a join, the name of the relation and the optional parent
of the document must be provided in the `source`.
For instance the following creates a parent document in the `my_parent` context:
[source,js]
--------------------------------------------------
PUT my_index/doc/1?refresh
{
"text": "This is a parent document",
"my_join_field": "my_parent" <1>
}
PUT my_index/doc/2?refresh
{
"text": "This is a another parent document",
"my_join_field": "my_parent"
}
--------------------------------------------------
// CONSOLE
// TEST[continued]
<1> This document is a `my_parent` document.
When indexing a child, the name of the relation as well as the parent id of the document
must be added in the `_source`.
It is required to index the lineage of a parent in the same shard so you must
always route child documents using their greater parent id.
For instance the following index two children documents pointing to the same parent
with a `routing` value equals to the `id` of the parent:
[source,js]
--------------------------------------------------
PUT my_index/doc/3?routing=1&refresh <1>
{
"text": "This is a child document",
"my_join_field": {
"name": "my_child", <2>
"parent": "1" <3>
}
}
PUT my_index/doc/4?routing=1&refresh <1>
{
"text": "This is a another child document",
"my_join_field": {
"name": "my_child",
"parent": "1"
}
}
--------------------------------------------------
// CONSOLE
// TEST[continued]
<1> This child document must be on the same shard than its parent
<2> `my_child` is the name of the join for this document
<3> The parent id of this child document
==== Parent-join restrictions
* Only one `join` field is allowed per index mapping.
* An element can have multiple children but only one parent.
* Parent and child documents must be indexed on the same shard.
This means that the same `routing` value needs to be provided when
<<docs-get,getting>>, <<docs-delete,deleting>>, or <<docs-update,updating>>
a child document.
* It is possible to add a new relation to an existing `join` field.
* It is also possible to add a child to an existing element
but only if the element is already a parent.
==== Searching with parent-join
The parent-join creates one field to index the name of the relation
within the document (`my_parent`, `my_child`, ...).
It also creates one field per parent/child relation. The name of this field is
the name of the `join` field followed by `#` and the name of the parent in the relation.
So for instance for the `my_parent` => [`my_child`, `another_child`] relation,
the `join` field creates an additional field named `my_join_field#my_parent`.
This field contains the parent `_id` that the document links to
if the document is a child (`my_child` or `another_child`) and the `_id` of
document if it's a parent (`my_parent`).
When searching an index that contains a `join` field, these two fields are always
returned in the search response:
[source,js]
--------------------------
GET my_index/_search
{
"query": {
"match_all": {}
},
"sort": ["_id"]
}
--------------------------
// CONSOLE
// TEST[continued]
[source,js]
--------------------------------------------------
{
...,
"hits": {
"total": 4,
"max_score": null,
"hits": [
{
"_index": "my_index",
"_type": "doc",
"_id": "1",
"_score": null,
"_source": {
"text": "This is a parent document",
"my_join_field": "my_parent"
},
"fields": {
"my_join_field": [
"my_parent" <1>
]
},
"sort": [
"1"
]
},
{
"_index": "my_index",
"_type": "doc",
"_id": "2",
"_score": null,
"_source": {
"text": "This is a another parent document",
"my_join_field": "my_parent"
},
"fields": {
"my_join_field": [
"my_parent" <2>
]
},
"sort": [
"2"
]
},
{
"_index": "my_index",
"_type": "doc",
"_id": "3",
"_score": null,
"_routing": "1",
"_source": {
"text": "This is a child document",
"my_join_field": {
"name": "my_child", <3>
"parent": "1" <4>
}
},
"fields": {
"my_join_field": [
"my_child"
],
"my_join_field#my_parent": [
"1"
]
},
"sort": [
"3"
]
},
{
"_index": "my_index",
"_type": "doc",
"_id": "4",
"_score": null,
"_routing": "1",
"_source": {
"text": "This is a another child document",
"my_join_field": {
"name": "my_child",
"parent": "1"
}
},
"fields": {
"my_join_field": [
"my_child"
],
"my_join_field#my_parent": [
"1"
]
},
"sort": [
"4"
]
}
]
}
}
--------------------------------------------------
// TESTRESPONSE[s/\.\.\./"timed_out": false, "took": $body.took, "_shards": $body._shards/]
<1> This document belongs to the `my_parent` join
<2> This document belongs to the `my_parent` join
<3> This document belongs to the `my_child` join
<4> The linked parent id for the child document
==== Parent-join queries and aggregations
See the <<query-dsl-has-child-query,`has_child`>> and
<<query-dsl-has-parent-query,`has_parent`>> queries,
the <<search-aggregations-bucket-children-aggregation,`children`>> aggregation,
and <<parent-child-inner-hits,inner hits>> for more information.
The value of the `join` field is accessible in aggregations
and scripts, and may be queried with the
<<query-dsl-parent-id-query, `parent_id` query>>:
[source,js]
--------------------------
GET my_index/_search
{
"query": {
"parent_id": { <1>
"type": "my_child",
"id": "1"
}
},
"aggs": {
"parents": {
"terms": {
"field": "my_join_field#my_parent", <2>
"size": 10
}
}
},
"script_fields": {
"parent": {
"script": {
"source": "doc['my_join_field#my_parent']" <3>
}
}
}
}
--------------------------
// CONSOLE
// TEST[continued]
<1> Querying the `parent id` field (also see the <<query-dsl-has-parent-query,`has_parent` query>> and the <<query-dsl-has-child-query,`has_child` query>>)
<2> Aggregating on the `parent id` field (also see the <<search-aggregations-bucket-children-aggregation,`children`>> aggregation)
<3> Accessing the parent id` field in scripts
==== Global ordinals
The `join` field uses <<eager-global-ordinals,global ordinals>> to speed up joins.
Global ordinals need to be rebuilt after any change to a shard. The more
parent id values are stored in a shard, the longer it takes to rebuild the
global ordinals for the `join` field.
Global ordinals, by default, are built eagerly: if the index has changed,
global ordinals for the `join` field will be rebuilt as part of the refresh.
This can add significant time to the refresh. However most of the times this is the
right trade-off, otherwise global ordinals are rebuilt when the first parent-join
query or aggregation is used. This can introduce a significant latency spike for
your users and usually this is worse as multiple global ordinals for the `join`
field may be attempt rebuilt within a single refresh interval when many writes
are occurring.
When the `join` field is used infrequently and writes occur frequently it may
make sense to disable eager loading:
[source,js]
--------------------------------------------------
PUT my_index
{
"mappings": {
"doc": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"my_parent": "my_child"
},
"eager_global_ordinals": false
}
}
}
}
}
--------------------------------------------------
// CONSOLE
The amount of heap used by global ordinals can be checked per parent relation
as follows:
[source,sh]
--------------------------------------------------
# Per-index
GET _stats/fielddata?human&fields=my_join_field#my_parent
# Per-node per-index
GET _nodes/stats/indices/fielddata?human&fields=my_join_field#my_parent
--------------------------------------------------
// CONSOLE
// TEST[continued]
==== Multiple levels of parent join
It is also possible to define multiple children for a single parent:
[source,js]
--------------------------------------------------
PUT my_index
{
"mappings": {
"doc": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"my_parent": ["my_child", "another_child"] <1>
}
}
}
}
}
}
--------------------------------------------------
// CONSOLE
<1> `my_parent` is parent of `my_child`.
... and multiple levels of parent/child:
[source,js]
--------------------------------------------------
PUT my_index
{
"mappings": {
"doc": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"my_parent": ["my_child", "another_child"], <1>
"another_child": "grand_child" <2>
}
}
}
}
}
}
--------------------------------------------------
// CONSOLE
<1> `my_parent` is parent of `my_child` and `another_child`
<2> `another_child` is parent of `grand_child`
The mapping above represents the following tree:
my_parent
/ \
/ \
my_child another_child
|
|
grand_child
Indexing a grand child document requires a `routing` value equals
to the grand-parent (the greater parent of the lineage):
[source,js]
--------------------------------------------------
PUT my_index/doc/3?routing=1&refresh <1>
{
"text": "This is a grand child document",
"my_join_field": {
"name": "grand_child",
"parent": "2" <2>
}
}
--------------------------------------------------
// CONSOLE
// TEST[continued]
<1> This child document must be on the same shard than its grandparent and parent
<2> The parent id of this document (must points to an `another_child` document)

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@ -1,7 +1,7 @@
[[search-request-inner-hits]]
=== Inner hits
The <<mapping-parent-field, parent/child>> and <<nested, nested>> features allow the return of documents that
The <<mapping-parent-join-field, parent-join> and <<nested, nested>> features allow the return of documents that
have matches in a different scope. In the parent/child case, parent documents are returned based on matches in child
documents or child documents are returned based on matches in parent documents. In the nested case, documents are returned
based on matches in nested inner objects.
@ -103,11 +103,11 @@ PUT test/doc/1?refresh
"comments": [
{
"author": "kimchy",
"text": "comment text"
"number": 1
},
{
"author": "nik9000",
"text": "words words words"
"number": 2
}
]
}
@ -118,7 +118,7 @@ POST test/_search
"nested": {
"path": "comments",
"query": {
"match": {"comments.text" : "words"}
"match": {"comments.number" : 2}
},
"inner_hits": {} <1>
}
@ -137,29 +137,29 @@ An example of a response snippet that could be generated from the above search r
...,
"hits": {
"total": 1,
"max_score": 1.0444683,
"max_score": 1.0,
"hits": [
{
"_index": "test",
"_type": "doc",
"_id": "1",
"_score": 1.0444683,
"_score": 1.0,
"_source": ...,
"inner_hits": {
"comments": { <1>
"hits": {
"total": 1,
"max_score": 1.0444683,
"max_score": 1.0,
"hits": [
{
"_nested": {
"field": "comments",
"offset": 1
},
"_score": 1.0444683,
"_score": 1.0,
"_source": {
"author": "nik9000",
"text": "words words words"
"number": 2
}
}
]
@ -425,33 +425,39 @@ This indirect referencing is only supported for nested inner hits.
[[parent-child-inner-hits]]
==== Parent/child inner hits
The parent/child `inner_hits` can be used to include parent or child
The parent/child `inner_hits` can be used to include parent or child:
[source,js]
--------------------------------------------------
PUT test
{
"settings": {
"mapping.single_type": false
},
"mappings": {
"my_parent": {},
"my_child": {
"_parent": {
"type": "my_parent"
"doc": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"my_parent": "my_child"
}
}
}
}
}
}
PUT test/my_parent/1?refresh
PUT test/doc/1?refresh
{
"test": "test"
"number": 1,
"my_join_field": "my_parent"
}
PUT test/my_child/1?parent=1&refresh
PUT test/doc/2?routing=1&refresh
{
"test": "test"
"number": 1,
"my_join_field": {
"name": "my_child",
"parent": "1"
}
}
POST test/_search
@ -461,7 +467,7 @@ POST test/_search
"type": "my_child",
"query": {
"match": {
"test": "test"
"number": 1
}
},
"inner_hits": {} <1>
@ -478,40 +484,59 @@ An example of a response snippet that could be generated from the above search r
[source,js]
--------------------------------------------------
{
...,
"hits": {
"total": 1,
"max_score": 1.0,
"hits": [
{
"_index": "test",
"_type": "my_parent",
"_id": "1",
"_score": 1.0,
"_source": ...,
"inner_hits": {
"my_child": {
"hits": {
"total": 1,
"max_score": 0.18232156,
"hits": [
{
"_type": "my_child",
"_id": "1",
"_score": 0.18232156,
"_routing": "1",
"_parent": "1",
"_source": {
"test": "test"
}
...,
"hits": {
"total": 1,
"max_score": 1.0,
"hits": [
{
"_index": "test",
"_type": "doc",
"_id": "1",
"_score": 1.0,
"_source": {
"number": 1,
"my_join_field": "my_parent"
},
"fields": {
"my_join_field": [
"my_parent"
]
},
"inner_hits": {
"my_child": {
"hits": {
"total": 1,
"max_score": 1.0,
"hits": [
{
"_type": "doc",
"_id": "2",
"_score": 1.0,
"_routing": "1",
"_source": {
"number": 1,
"my_join_field": {
"name": "my_child",
"parent": "1"
}
},
"fields": {
"my_join_field": [
"my_child"
],
"my_join_field#my_parent": [
"1"
]
}
}
]
}
}
}
]
}
}
}
}
]
}
]
}
}
--------------------------------------------------
// TESTRESPONSE[s/"_source": \.\.\./"_source": $body.hits.hits.0._source/]