Tag - EXPLAIN FORMAT=JSON

Introduction to Troubleshooting Performance – Troubleshooting Slow Queries webinar: Q & A

InnoDB Troubleshooting

In this blog, I will provide answers to the Q & A for the Troubleshooting Slow Queries webinar.
First, I want to thank you for attending the April 28 webinar. The recording and slides for the webinar are available here. Below is the list of your questions that I wasn’t able to answer during the webinar, with […]

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EXPLAIN FORMAT=JSON wrap-up

EXPLAIN FORMAT=JSON

This blog is an EXPLAIN FORMAT=JSON wrap-up for the series of posts I’ve done in the last few months.
In this series, we’ve discussed everything unique to
EXPLAIN FORMAT=JSON. I intentionally skipped a description of members such as
table_name,
access_type  or
select_id, which are not unique.
In this series, I only mentioned in passing members that […]

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EXPLAIN FORMAT=JSON: cost_info knows why optimizer prefers one index to another

Percona Server 5.7 performance improvements

Time for another entry in the EXPLAIN FORMAT=JSON is cool! series of blog posts. This time we’ll discuss how using EXPLAIN FORMAT=JSON allows you to see that
cost_info  knows why the optimizer prefers one index to another.
Tables often have more than one index. Any of these indexes can be used to resolve query. The optimizer has […]

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EXPLAIN FORMAT=JSON has details for subqueries in HAVING, nested selects and subqueries that update values

Over several previous blog posts, we’ve already discussed what information the 
EXPLAIN FORMAT=JSON output provides for some subqueries. You can review those discussions here, here and here. EXPLAIN FORMAT=JSON shows many details that you can’t get with other commands. Let’s now finish this topic and discuss the output for the rest of the subquery types.
First, let’s look at the […]

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EXPLAIN FORMAT=JSON: order_by_subqueries, group_by_subqueries details on subqueries in ORDER BY and GROUP BY

EXPLAIN FORMAT=JSON

Another post in the EXPLAIN FORMAT=JSON is Cool! series! In this post, we’ll discuss how the EXPLAIN FORMAT=JSON provides optimization details for 
ORDER BY and  
GROUP BY operations in conjunction with 
order_by_subqueries and  
group_by_subqueries. 

EXPLAIN FORMAT=JSON can print details on how a subquery in
ORDER BY is optimized:

MySQL

mysql> explain format=json select emp_no, concat(first_name, ‘ ‘, last_name) f2 from employees order by (select emp_no limit 1)G
*************************** 1. […]

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