Showing entries 1 to 4
Displaying posts with tag: query optimizer (reset)
The MySQL 5.7 Optimizer Challenge

In the MySQL team, we have been working really hard on refactoring the optimizer and improving the cost model. The hacks of storage engines lying to the optimizer are being rolled back, and your chances of getting an optimal query plan should now be much higher than in prior releases of MySQL.

The optimizer team has also allowed cost constants to be configurable on both a server and a storage engine basis, and we are confident that the default InnoDB engine will always work “as good as MyISAM” (which has a natural advantage, in that the optimizer was originally largely built around it.)

Today, I want to issue a challenge:

Find an example where the …

[Read more]
Optimizer Trace and EXPLAIN FORMAT=JSON in 5.7

I accidentally stumbled upon this Stack Overflow question this morning:

I am wondering if there is any difference in regards to performance between the following:

SELECT ... FROM ... WHERE someFIELD IN(1,2,3,4);
SELECT ... FROM ... WHERE someFIELD between  0 AND 5;
SELECT ... FROM ... WHERE someFIELD = 1 OR someFIELD = 2 OR someFIELD = 3 ...;

It is an interesting question because there was no good way to answer it when it was asked in 2009. All of the queries resolve to the same output in EXPLAIN. Here is an example using the sakila schema:

mysql> EXPLAIN SELECT * FROM film WHERE film_id IN (1,2,3,4,5)\G
mysql> EXPLAIN SELECT * FROM film WHERE film_id =1 or film_id=2 or film_id=3 or film_id=4 or film_id=5\G
********* 1. row *********
           id: 1 …
[Read more]
Testing the UNION ALL Optimization in MySQL 5.7 DMR3

When MySQL 5.7 DMR3 was released, I couldn’t wait to try out the new UNION ALL optimization that no longer requires data to be materialized in a temporary table.

This new optimization can be seen via EXPLAIN, but it is also nice to run it through SHOW PROFILES, which breaks down query execution step by step. However, this feature is now deprecated (since it overlaps with performance_schema), and will be removed in a future version.

So today I wanted to show you a combination of: * What a UNION ALL statement looks like in MySQL 5.6 (EXPLAIN, SHOW PROFILES). * How it is improved in MySQL 5.7 (EXPLAIN, SHOW PROFILES). * How you can easily emulate the SHOW PROFILES feature with performance_schema + ps_helper

[Read more]
Shoot in the foot

I've just finished reading two recent blog posts about new query optimizations in the upcoming MySQL 6.0, it's all fine and dandy but ...Looking at Correlated semi-join subqueries and PostgreSQL by S. Petrunia we can read something like Quote: The first thing we did was to take a look at PostgreSQL as it is easily available and seems to have at least decent subquery handling (or even better

Showing entries 1 to 4