After I updated a Fedora 30 instance, I could no longer connect to the MySQL database. An attempt to connect raised the following error:

Error: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

My guess was correct, the mysqld.service got removed during the update (a synonym for upgrade). So, I ran the following command as a sudoer user:

sudo systemctl enable mysqld.service

It creates the following symbolic link:

Created symlink /etc/systemd/system/multi-user.target.wants/mysqld.service → /usr/lib/systemd/system/mysqld.service.

That would start the MySQL Daemon (mysqld) on the next restart of the OS. However, I didn’t want to restart to have access to the service. I simply started it with the following command:

sudo systemctl start mysqld.service

Then, I could connect to the MySQL database. As always, …

My students want to transfer their course setup MySQL files from the Linux VM that I provide to Microsoft Windows 10. This post explains how because I found a couple small errors in the Google’d posts they would most likely see.

The first step is required because when I didn’t assign a name or domain to the the Fedora VM, which allows it to run as localhost on any student machine. In tandem, I didn’t assign a static IP address but opted for dynamic IP assignment. That means, the first step to securely copy the files requires you to find the assigned IP address. You can do that with the following Linux command:

ifconfig -a | grep 'inet[[:blank:]]' | head -1 | cut -c 14-30

It would return something like:

192.168.147.198

After you have discovered the IP address, you need to download PuTTy from their web site because includes the pscp (PuTTy …

It’s the in-between term time and we’re all stuck at home. I decided to update the image for my Fedora 30 virtual machine. I had a work around to the update issue that I had encountered last October in Bug #96969 but it was not required with the current version. However, after updating from MySQL 8.0.17 to MySQL 8.0.19, I found that my Java connection example failed.

The $CLASSPATH value was correct:

/usr/share/java/mysql-connector-java.jar:.

The first error that I got was the my reference to MySQL JDBC driver was incorrect. The error message is quite clear:

Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
Cannot connect to database server:
The server time zone …

In this post I’ll expand on the subject of my MySQL pre-FOSDEM talk: what dbadmins need to know and do, when upgrading from MySQL 5.7 to 8.0.

I’ve already published two posts on two specific issues; in this article, I’ll give the complete picture.

As usual, I’ll use this post to introduce tooling concepts that may be useful in generic system administration.

The presentation code is hosted on a GitHub repository (including the …

FEMP is an acronym that stands for FreeBSD (operating system), Nginx (HTTP server pronounced Engine-x), MySQL (database server), and PHP (programming language to process dynamic PHP content). In this tutorial, we'll set up components of a FEMP stack on a FreeBSD 12.1 server using pkg, the FreeBSD package manager.

Starting with version 8.0.18 the MySQL Workbench source package finally ships also all our GPL unit and integration tests, which we are using internally to control code quality. For that we had first to replace our old, outdated testing framework by something new and more appropriate. We evaluated quite a few C++ testing frameworks but found them either not to be sufficient or difficult to use. Instead we had something in mind that comes close to the Jasmine framework which is widely used among JS developers. The way it hides all the boring test management details and the clear structure it uses, was quite an inspiration for us and we decided to develop our own testing framework modeled after that.

Casmine – C++17 BDD Testing Framework

Casmine is a C++ unit and integration testing …

Recently, at Percona Live Europe 2019, Dimitri Kravchuk from Oracle mentioned that he observed some unclear drop in performance for MySQL on an ext4 filesystem with the latest Linux kernels. I decided to check this case out on my side and found out that indeed, starting from linux kernel 4.9, there are some cases with notable (up to 2x) performance drops for ext4 filesystem in direct i/o mode.

So what’s wrong with ext4? It started in 2016 from the patch that was pushed to kernel 4.9: “ext4: Allow parallel DIO reads”. The purpose of that patch was to help to improve read scalability in direct i/o mode. However, along with improvements in pure read workloads, it also introduced regression in intense mixed random read/write scenarios. And it’s quite weird, but this issue had not been …

Its not the new term for DBAs. MySQL has an awesome parameter innodb-file-per-tables allows MySQL to create separate files for each tables. This helped a lot to manage the disk space in more efficient way. But when we perform a large batch job for delete or update the data in MySQL tables, you may face this fragmentation issue. Comparing with SQL server, MySQL’s fragmentation is not high. I had a similar situation where my Disk space was consuming 80% and when I check the huge files in OS, one table’s idb file consumed 300GB+. I know it has some wasted blocks(but not actually wasted, MySQL will use this space, it’ll not return this to OS) Then I checked the information schema to find out the data size and its index size. It was 27GB only. Then I realize, we did a batch operation to delete many billions of records in that table.

Thanks to Rolando - MySQL DBA:

When I searched the similar …

Somebody asked me how to expand a prior example with the static variables so that it took arguments at the command line for the variables. This example uses Python 3 new features in the datetime package.

There’s a small trick converting the string arguments to date data types. Here’s a quick example that shows you how to convert the argument list into individual date data type variables:

#!/usr/bin/python3

# include standard modules
import sys
from datetime import datetime

# Capture argument list.
fullCmdArguments = sys.argv

# Assignable variables.
beginDate = ""
endDate = ""

# Assign argument list to variable.
argumentList = fullCmdArguments[1:]

# Enumerate through the argument list where beginDate precedes endDate as strings.
try:
  for i, s in enumerate(argumentList):
    if (i == …

In this short blog post, we will check how to use linux-fincore to check which files are in the in-memory Linux page cache. To have an introductory read about the Linux page cache check here and here.

In summary, whenever you read from or write to a file (unless you are using Direct_IO to bypass the functionality), the result is cached in memory, so that subsequent requests can be served from it, instead of the orders of magnitude-slower disk subsystem (it can also be used to cache writes, before flushing them to disk). This is done as far as there is memory that is not being used by any process; whenever there is a shortage of otherwise free memory, the kernel will choose to first evict the page cache …