The latest from the MySQL community

We all tried various alternative methods for modifying the table structure, but pt-online-schema-change (pt-osc) is the most convenient and preferred method for performing the alter online. It has more granular control too. But it may lead to data loss if proper precautionary steps are not taken care of.

In this blog, we are going to modify a column to a unique key using pt-osc, below I have shared the table structure.

mysql> show create table test\G
* 1. row *
Table: test
Create Table: CREATE TABLE test (
Personid int(11) NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255) DEFAULT NULL,
Age int(11) DEFAULT NULL,
PRIMARY KEY (Personid)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

I have inserted the data of 1000 rows using …

Generally, most all web applications are going to follow the elements of CRUD: Create, Read, Update, and Delete. CodeIgniter 4 is a powerful PHP web development framework that provides a rapid development environment. The CodeIgniter 4 Models come enriched with built-in CRUD functionality, which is covered in this compilation of Medium posts…

Image by Dariusz Sankowski from Pixabay 

Disclaimer: I originally published these articles first over on …

Well, let me say if that happens it’s because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short, the WHY of this article is to inform you about possible pitfalls and how to prevent them from causing you damage.

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from the MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing …

Well, let me say if that happens because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short the WHY of this article is to inform you about possible pitfalls and how to prevent that to cause you damage. 

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing queries at the …

Well, let me say if that happens because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short the WHY of this article is to inform you about possible pitfalls and how to prevent that to cause you damage. 

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing queries at the …

At work, replication

is a central feature in our MySQL Standard Architecture.

But until MySQL 5.6, replication was strictly sequential: Even if transactions happened in parallel on a primary, they would be downloaded to the replica by the IO_THREAD into the relay log. From there, a single SQL_THREAD would apply them, one after the other in strict binlog order. That can lead to Replication Delay.

We had a monitor for that, courtesy of Dennis Kaarsemaker

. That code looked at the time consumption in the SQL_THREAD, and counted the percentage of idle time over time, visualizing it in Graphite or Grafana.

This was the amount of runway we had. If the write-load to a specific replication hierarchy threatened to …

As a developer using Python, I want to be able to hand a list to an SQL statement with a WHERE id IN (…) clause, and it should do the right thing.

Well, that is not how it started, because it was asked on the internal no-work-channel, so it kind of escalated more.

A question

The original question was:

Dev> Why is it 2021, and SQL prepared statements still can’t deal with IN? Or have I missed some exciting development?

After a quick detour through Java (which we won’t discuss any further in this article), we established that this was a Python problem in this particular instance. And we touched on several other interesting things on our way.

But first, the solution:

#! /usr/bin/env python3

import click
import MySQLdb
import MySQLdb.cursors

class …

As a developer using Python, I want to be able to hand a list to an SQL statement with a WHERE id IN (…) clause, and it should do the right thing.

Well, that is not how it started, because it was asked on the internal no-work-channel, so it kind of escalated more.

A question

The original question was:

Dev> Why is it 2021, and SQL prepared statements still can’t deal with IN? Or have I missed some exciting development?

After a quick detour through Java (which we won’t discuss any further in this article), we established that this was a Python problem in this particular instance. And we touched on several other interesting things on our way.

But first, the solution:

#! /usr/bin/env python3

import click
import MySQLdb
import MySQLdb.cursors

class DebugCursor(MySQLdb.cursors.DictCursor):
    def _query(self, q):
        print(f"Debug: {q}") …

     Histograms were introduced with MySQL 8.0 and are a valuable way of speeding up queries.  The MySQL optimizer assumes that data in a column has evenly distributed values. Even distribution of data probably does not reflect much of the data sitting right now in your database.  

    The optimizer wants to find the most efficient way to return the data requested in a query.  If it has poor information on that data, then the optimizer will make a 'guesstimate' that will will result in a query plan that will not perform well.  But if the optimizer has good information, in this case provided by a histogram, then it can produce a better query plan.

    In the following example a able is filled with data that is not evenly distributed.  In the histogram image following, the data is represented in what looks like a rollercoaster side view. 
…

I use CodeIgniter 4 a great deal for learning, personal projects, and application development. In this post, I cover 2 different methods you can use and retrieve the MySQL Last Insert ID value after executing an INSERT statement in CodeIgniter. Continue reading for more information…

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Model Setup

Starting out, I use the CLI Generator feature and create a Model by executing this code in the terminal in the project root:

php spark make:model user --suffix

I have removed much of the …