In MySQL 5.7 we are planning to deprecate the syntax:

EXPLAIN PARTITIONS <insert query here>
EXPLAIN EXTENDED <insert query here>

.. and enable these two options by default.

The rationale is that:

  • Simple and consistent is always better. EXPLAIN FORMAT=JSON already behaves like these two flags are enabled, and if you have a partitioned table for example, it is unlikely that you would not want the PARTITIONS option. Having to remember two more flags makes the product harder to use.

  • The optimizer team has been busy refactoring and improving code quality. These two flags are supported by many if-statements, increasing complexity by more than we would like.

The intended deprecation plan is to automatically turn both flags on in MySQL 5.7 and issue deprecation warnings when using the older syntax. In MySQL 5.8, the syntax will be removed.

What do I expect will break?

That's a good question, since EXPLAIN is really a DBA tool, and is unlikely to affect running applications. I expect it to be:

  • Automated tools that depend on column order of EXPLAIN, or EXPLAIN not producing a warning (as of MySQL 5.7).

  • Automated tools that explicitly use EXPLAIN PARTITIONS or EXPLAIN EXTENDED (as of MySQL 5.8).

Both I hope should be fairly simple fixes.

How can I make my tools more resilient?

While we're on the subject of EXPLAIN and automated tools, it is a good segway to lead into EXPLAIN FORMAT=JSON, which is very well suited here. I would expect that with JSON output, applications are more likely to be able to tolerate changes to the information returned and in MySQL 5.7 the JSON is already much more detailed.

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I joined MySQL AB in 2006, left, and am now back at Oracle working on the MySQL team. I've also worked at Percona and InPowered.

  • http://karwin.blogspot.com Bill Karwin

    Agree that simple and consistent is better. It would also be nice to create a global or session config variable so I could run `SET {SESSION|GLOBAL} explain_format=JSON` and get that output without having to specify the optional syntax every time.

    • http://www.tocker.ca/ Morgan Tocker

      Do you mind filing this as a feature request in bugs.mysql.com?

      I think this could be incredibly useful. I know I would enable it for my MySQL CLI sessions.

  • Shlomi Noach

    Good call