docs: document explain api (close #870) (#3739)

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.. _explain_api_reference:
Explain API Reference
=====================
.. contents:: Table of contents
:backlinks: none
:depth: 1
:local:
The Explain API is used to analyse queries and subscriptions. It returns a list of Postgres plans for a query and a single Postgres plan for a subscription, based
on the defined permissions.
Endpoint
--------
All requests are ``POST`` requests to the ``/v1/graphql/explain`` endpoint.
API Spec
--------
Request
^^^^^^^
The request expects a JSON object with the following keys:
- ``query``: the GraphQL query to be analysed
- ``user`` (optional): the ``x-hasura-role`` along with session variables
.. code-block:: http
POST /v1/graphql/explain HTTP/1.1
Content-Type: application/json
{
"query": <query>,
"user": {
"x-hasura-role" : "...",
"x-hasura-session-var1" : "..."
}
}
Sample request
**************
.. code-block:: http
POST /v1/graphql/explain HTTP/1.1
Content-Type: application/json
{
"query": {
"query": "query getAuthors { authors { name }}",
"operationName": "getAuthors"
}
}
Response
^^^^^^^^
The response for a query is a list of plans:
.. code-block:: json
[
{
"field": String -- "name of the field",
"sql": String -- "the generated SQL for the operation",
"plan": [String] -- "Postgres's plan for the generated SQL"
}
]
The response for a subscription is a single plan:
.. code-block:: json
{
"sql": String -- "the generated SQL for the operation",
"plan": [String] -- "Postgres's plan for the generated SQL"
}
Sample response for a query
***************************
.. code-block:: json
[
{
"field": "authors",
"sql": "SELECT coalesce(json_agg(\"root\" ), '[]' ) AS \"root\" FROM (SELECT row_to_json((SELECT \"_1_e\" FROM (SELECT \"_0_root.base\".\"name\" AS \"name\" ) AS \"_1_e\" ) ) AS \"root\" FROM (SELECT * FROM \"public\".\"authors\" WHERE ('true') ) AS \"_0_root.base\" ) AS \"_2_root\" ",
"plan": [
"Aggregate (cost=14.27..14.27 rows=1 width=32)",
" -> Seq Scan on authors (cost=0.00..11.83 rows=610 width=32)",
" SubPlan 1",
" -> Result (cost=0.00..0.00 rows=1 width=32)"
]
}
]
Sample response for a subscription
**********************************
.. code-block:: json
{
"sql": "\n select\n _subs.result_id, _fld_resp.root as result\n from\n unnest(\n $1::uuid[], $2::json[]\n ) _subs (result_id, result_vars)\n left outer join lateral\n (\n SELECT coalesce(json_agg(\"root\" ), '[]' ) AS \"root\" FROM (SELECT row_to_json((SELECT \"_1_e\" FROM (SELECT \"_0_root.base\".\"name\" AS \"name\" ) AS \"_1_e\" ) ) AS \"root\" FROM (SELECT * FROM \"public\".\"authors\" WHERE ('true') ) AS \"_0_root.base\" ) AS \"_2_root\" \n ) _fld_resp ON ('true')\n ",
"plan": [
"Nested Loop Left Join (cost=14.27..14.93 rows=100 width=48)",
" -> Function Scan on _subs (cost=0.00..0.30 rows=100 width=16)",
" -> Materialize (cost=14.27..14.28 rows=1 width=32)",
" -> Aggregate (cost=14.27..14.27 rows=1 width=32)",
" -> Seq Scan on authors (cost=0.00..11.83 rows=610 width=32)",
" SubPlan 1",
" -> Result (cost=0.00..0.00 rows=1 width=32)"
]
}
Disabling Explain API
---------------------
The Explain API is part of the :doc:`Metadata API <schema-metadata-api/index>` and can only be disabled by disabling the same.

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@ -15,23 +15,25 @@ API Reference
Available APIs
--------------
+-----------------+----------------------------------------+------------------+
| API | Endpoint | Access |
+=================+========================================+==================+
| GraphQL | :ref:`/v1/graphql <graphql_api>` | Permission rules |
+-----------------+----------------------------------------+------------------+
| Legacy GraphQL | :ref:`/v1alpha1/graphql <graphql_api>` | Permission rules |
+-----------------+----------------------------------------+------------------+
| Schema/Metadata | :ref:`/v1/query <schema_metadata_api>` | Admin only |
+-----------------+----------------------------------------+------------------+
| Version | :ref:`/v1/version <version_api>` | Public |
+-----------------+----------------------------------------+------------------+
| Health | :ref:`/healthz <health_api>` | Public |
+-----------------+----------------------------------------+------------------+
| PG Dump | :ref:`/v1alpha1/pg_dump <pg_dump_api>` | Admin only |
+-----------------+----------------------------------------+------------------+
| Config | :ref:`/v1alpha1/config <config_api>` | Admin only |
+-----------------+----------------------------------------+------------------+
+-----------------+-----------------------------------------+------------------+
| API | Endpoint | Access |
+=================+=========================================+==================+
| GraphQL | :ref:`/v1/graphql <graphql_api>` | Permission rules |
+-----------------+-----------------------------------------+------------------+
| Legacy GraphQL | :ref:`/v1alpha1/graphql <graphql_api>` | Permission rules |
+-----------------+-----------------------------------------+------------------+
| Schema/Metadata | :ref:`/v1/query <schema_metadata_api>` | Admin only |
+-----------------+-----------------------------------------+------------------+
| Version | :ref:`/v1/version <version_api>` | Public |
+-----------------+-----------------------------------------+------------------+
| Health | :ref:`/healthz <health_api>` | Public |
+-----------------+-----------------------------------------+------------------+
| PG Dump | :ref:`/v1alpha1/pg_dump <pg_dump_api>` | Admin only |
+-----------------+-----------------------------------------+------------------+
| Config | :ref:`/v1alpha1/config <config_api>` | Admin only |
+-----------------+-----------------------------------------+------------------+
| Explain | :ref:`/v1/graphql/explain <explain_api>`| Admin only |
+-----------------+-----------------------------------------+------------------+
.. _graphql_api:
@ -94,6 +96,16 @@ configuration.
See details at :doc:`config`.
.. _explain_api:
Explain API
^^^^^^^^^^^
``v1/graphql/explain`` returns the Postgres plan for a query or subscription based
on the defined permissions.
See details at :doc:`explain`.
Supported PostgreSQL types
--------------------------
You can refer to the following to know about all PostgreSQL types supported by the Hasura GraphQL engine:
@ -110,4 +122,5 @@ You can refer to the following to know about all PostgreSQL types supported by t
Health check API <health>
PG Dump API <pgdump>
Config API <config>
Explain API <explain>
Supported PostgreSQL types <postgresql-types>