EXPLAIN FORMAT=JSON in MySQL - Source

Revision: 130907
User: Sergei Petrunia
Date: 2015-12-09 20:33

<<toc>>

There are some things that we in MariaDB are not happy with in MySQL/Oracle's implementation of EXPLAIN FORMAT=JSON.

The most important issues are already fixed in MariaDB's [[explain-format-json|EXPLAIN FORMAT=JSON]] implementation. See [[explain-format-json-differences|EXPLAIN FORMAT=JSON Differences From MySQL]] for details.

This page lists things are are not fixed yet.

== Higher priority
* Better display for ORDER/GROUP BY (MDEV-6995)
* Better display for Batched Key Access plans (Plain join buffering is fixed already)

== Nice to have
=== Show ranges being scanned
Currently, one can only find the ranges produced by the range optimizer by looking into optimizer_trace. It would be nice if EXPLAIN showed them, too

<<code>>
MySQL [dbt3sf1]> explain format=json select * from customer where c_acctbal < -1000 \G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "customer",
      "access_type": "range",
      "possible_keys": [
        "c_acctbal",
        "i_c_acctbal_nationkey"
      ],
      "key": "c_acctbal",
      "used_key_parts": [
        "c_acctbal"
      ],
      "key_length": "9",
      "rows": 1,
      "filtered": 100,
      "index_condition": "(`dbt3sf1`.`customer`.`c_acctbal` < -(1000))"
    }
  }
}
<</code>>

== Low priority

=== Filesort/priority queue
Neither version of EXPLAIN in 5.6 shows the "filesort with small limit" optimization. See MDEV-6430.

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EXPLAIN FORMAT=JSON in MySQL - Source

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