This is the second part of a two parts series. In MongoDB: index usage and MongoDB explain() we introduced the main index types supported by MongoDB, and how to create and use them. In this second article, we are going to see some examples on how to use explain() method to investigate queries. Do […]Read more
Please join Percona’s MySQL Database Administrator, Brad Mickel as he presents How to Analyze and Tune MySQL Queries for Better Performance on Thursday, June 21st, 2018, at 10:00 AM PDT (UTC-7) / 1:00 PM EDT (UTC-4).
Query performance is essential in making any application successful. In order to finely tune your queries you first […]
Join Percona’s Senior Architect, Matthew Boehm, as he presents What You Need to Get the Most Out of Indexes – Part 2 webinar on Thursday, October 19, 2017, at 11:00 am PDT / 2:00 pm EDT (UTC-7).
Proper indexing is key to database performance. Finely tune your query writing and database performance with tips […]Read more
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 […]
Once again it’s time for another EXPLAIN FORMAT=JSON is cool! post. This post will discuss how EXPLAIN FORMAT=JSON allows the nested_loop command to make the JOIN operation hierarchy transparent.
EXPLAIN command lists each table that participates in a
JOIN operation on a single row. This works perfectly for simple queries:
mysql> explain select * from […]Read more
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 […]
Time for another entry in the EXPLAIN FORMAT=JSON is cool! series. Today we’re going to look at how you can view the buffer result using JSON (instead of the regular
EXPLAIN does not identify if
SQL_BUFFER_RESULT was used at all. To demonstrate, let’s run this query:
mysql> explain select * from salariesG
*************************** 1. row ***************************
Ready for another post in the EXPLAIN FORMAT=JSON is Cool series! Great! This post will discuss how to see all the information that is contained in optimized queries with
UNION using the
When optimizing complicated queries with
UNION, it is easy to get lost in the regular
EXPLAIN output trying to identify which part of […]
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 […]
We’ve already discussed using the ORDER BY clause with subqueries. You can also, however, use the
ORDER BY clause with sorting results of one of the columns. Actually, this is most common way to use this clause.
Sometimes such queries require using temporary tables or filesort, and a regular
EXPLAIN clause provides this information. But it doesn’t show if […]