Showing entries 1 to 10 of 85
10 Older Entries »
Displaying posts with tag: explain (reset)
MySQL EXPLAIN ANALYZE

As of MySQL 8.0.18, EXPLAIN ANALYZE is an indispensable tool for understanding query execution because it breaks down the query execution stage of response time by measuring each step of the query execution plan. The information is illuminating, but the output is not intuitive: it requires practice and some understanding of how MySQL executes queries beyond the table join order shown by traditional EXPLAIN output. This blog post closely examines three different examples of EXPLAIN ANALYZE output.

MySQL EXPLAIN ANALYZE

As of MySQL 8.0.18, EXPLAIN ANALYZE is an indispensable tool for understanding query execution because it breaks down the query execution stage of response time by measuring each step of the query execution plan. The information is illuminating, but the output is not intuitive: it requires practice and some understanding of how MySQL executes queries beyond the table join order shown by traditional EXPLAIN output. This blog post closely examines three different examples of EXPLAIN ANALYZE output.

MySQL EXPLAIN ANALYZE

As of MySQL 8.0.18, EXPLAIN ANALYZE is an indispensable tool for understanding query execution because it breaks down the query execution stage of response time by measuring each step of the query execution plan. The information is illuminating, but the output is not intuitive: it requires practice and some understanding of how MySQL executes queries beyond the table join order shown by traditional EXPLAIN output. This blog post closely examines three different examples of EXPLAIN ANALYZE output.

Why write a new planner

Query planning is hard # Have you ever wondered what goes on behind the scenes when you execute a SQL query? What steps are taken to access your data? In this article, I'll talk about the history of Vitess's V3 query planner, why we created a new query planner, and the development of the new Gen4 query planner. Vitess is a horizontally scalable database solution which means that a single table can be spread out across multiple database instances.

Examining query plans in MySQL and Vitess

Originally posted at Andres's blog. Traditional query optimizing is mostly about two things: first, in which order and from where to access data, and then how to then combine it. You have probably seen the tree shapes execution plans that are produced from query planning. I’ll use an example from the MySQL docs, using FORMAT=TREE which was introduced in MySQL 8.0: mysql>EXPLAINFORMAT=TREE->SELECT*->FROMt1->JOINt2->ON(t1.c1=t2.c1ANDt1.c2<t2.c2)->JOINt3->ON(t2.c1=t3.c1)\G***************************1.row***************************EXPLAIN:->Innerhashjoin(t3.c1=t1.c1)(cost=1.05rows=1)->Tablescanont3(cost=0.35rows=1)->Hash->Filter:(t1.c2<t2.c2)(cost=0.70rows=1)->Innerhashjoin(t2.c1=t1.c1)(cost=0.70rows=1)->Tablescanont2(cost=0.35rows=1)->Hash->Tablescanont1(cost=0.35rows=1)Here we can see that the MySQL optimizer thinks the best plan is to start reading from t1 using a table scan.

Webinar Thu 6/21: How to Analyze and Tune MySQL Queries for Better Performance

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).

Register Now

 

Query performance is essential in making any application successful. In order to finely tune your queries you first need to understand how MySQL executes them, and what tools are available to help identify problems.

In this session you will learn:

  1. The common tools for researching problem queries
  2. What an Index is, and why you should use one
  3. Index limitations
  4. When to rewrite the …
[Read more]
This Week in Data with Colin Charles 18: Percona Live Call For Papers and a MongoDB 3.6 Overview

Join Percona Chief Evangelist Colin Charles as he covers happenings, gives pointers and provides musings on the open source database community.

I highly recommend submitting to the CFP for Percona Live Santa Clara 2018 even though it only closes December 22 2017. By the 3rd week of December, i.e. before the CfP closes, it is very likely that we will announce some of the schedule. So get in early! Keep in mind the broad topics, there are some ideas here.

Also: we are looking for sponsors for Percona Live – you can email me for more information.

Releases

[Read more]
Webinar Thursday, October 19, 2017: What You Need to Get the Most Out of Indexes – Part 2

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).

Register Now

Proper indexing is key to database performance. Finely tune your query writing and database performance with tips from the experts. MySQL offers a few different types of indexes and uses them in a variety of ways.

In this session you’ll learn:

  • How to use composite indexes
  • Other index usages besides lookup
  • How to find …
[Read more]
Introduction to Troubleshooting Performance – Troubleshooting Slow Queries webinar: Q & A

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 responses:

Q: I’ve heard that is a bad idea to use

select *

; what do you recommend?

A: When I used

SELECT *

 in my slides, I wanted to underline the idea that sometimes you need to select all columns from …

[Read more]
EXPLAIN FORMAT=JSON wrap-up

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 replace information from the

Extra

 column in the regular

EXPLAIN

 output, such as

using_join_buffer

 ,

partitions

,

using_temporary_table

  or simply

[Read more]
Showing entries 1 to 10 of 85
10 Older Entries »