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Displaying posts with tag: hacks (reset)
Revisiting the hidden MySQL 8.0 data dictionary tables

A few months ago I wrote about showing the hidden tables in MySQL 8 data dictionary. What I presented there was a naïve solution, which I am now able to improve with a few (bold) moves. In the solution given in my previous article, I was able to guess the table names somehow, but they were still hidden from the catalog. I did not think clearly then. I should have used the data dictionary itself to see the tables. Here, in addition to getting the real list of tables, I offer a feature to unhide them permanently.

MySQL-Sandbox 3.2.08 has now the ability of un-hide the data dictionary tables, and keep them available for inspection. This feature came to my mind after a chat with the MySQL team during PerconaLive 2017. They stressed the …

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Turning 38 today; Going Static

I am turning 38 years old today. I am on my way to Belgium for the funeral of my grandmother. My family, Marta and Tomas, are at home.

I am in Bielefeld, on top of the hill. This is our usual stop from Berlin to Belgium: it’s practically in the middle.

I am sitting at the bar, and I have just finished a great project I have been working for a few months: revamp my homepage and blog, once again.

I tried a few things getting away from (the great) Wordpress. I was trying to make my own again, doing it with Django or Flask, I am a Python guy after all. I tried to do something with my OwnCloud setup, with files, but that was so 1990s, writing HTML.

Giving up, I did a search for “generate static website” and I pretty much hit the first link: “Jekyll”. It is written in Ruby, so I am …

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Quick and dirty concurrent operations from the shell

Let’s say that you want to measure something in your database, and for that you need several operations to happen in parallel. If you have a capable programming language at your disposal (Perl, Python, Ruby, PHP, or Java would fit the bill) you can code a test that sends several transactions in parallel.

But if all you have is the shell and the mysql client, things can be trickier. Today I needed such a parallel result, and I only had mysql and bash to accomplish the task.

In the shell, it’s easy to run a loop:

for N in $(seq 1 10)
mysql -h host1 -e "insert into sometable values($N)"

But this does run queries sequentially, and each session will open and close before the next one starts. Therefore there is no concurrency at all.
Then I thought that the method for parallel execution in the shell is to run things in the background, and then collect the …

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A few hacks to simulate mysqldump --ignore-database

A few days ago, Ronald Bradford asked for a mysqldump –ignore-database option.

As a workaround, he proposes:

mysqldump --databases `mysql --skip-column-names \
-e "SELECT GROUP_CONCAT(schema_name SEPARATOR ' ') \
FROM information_schema.schemata WHERE schema_name \
NOT IN ('mysql','performance_schema','information_schema');" \
>` >/mysql/backup/rds2.sql

It's a clever solution, but unfortunately it only works if you have a handful of schemas. If your databases happens to have several dozens (or hundreds or thousands) of schemas (which is where you need this option more), then the output will be truncated to the length of group_concat_max_len (by default, 1024.)

There are two alternative methods.

The all-shell methodThis method lets …

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21st century presentation technology at Percona Live

After 15 years of slide show technology, I thought that we need to change the way we do presentations. And since I am advocating radical changes, I will eat my own dog food and be the first to present a MySQL session using 3D technology.

Since watching Avatar a few years ago, I thought that using this technology would make my presentations truly amazing. However, two years ago a 3d projector was prohibitively expensive. Now, instead, it is affordable, and fits in my briefcase!

What I needed, though, was a compelling reason for using 3d vs. traditional presentations. And I found it. As I have mentioned recently, I am working with the coolest replication technology on earth. Explaining this technology is often challenging. While regular replication …

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Never say "there is no way"

Reading a recent MySQL book, I saw an example of SHOW CREATE TABLE that comes with backticks (`) around the table and column names, and a comment:
Unfortunately, there is no way to remove this from generated syntax with this command.(Emphasis mine).
Here's how it goes:

mysql> show create table mytest\G
*************************** 1. row ***************************
Table: mytest
Create Table: CREATE TABLE `mytest` (
`id` int(11) NOT NULL,
`description` varchar(50) DEFAULT NULL,
1 row in set (0.00 sec)

Of course, there is a way!

mysql> pager tr -d '`'
PAGER set to 'tr -d '`''
mysql> show create table mytest\G
*************************** 1. row ***************************
Table: mytest
Create Table: CREATE TABLE …
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Reading results of SHOW statements, on server side

SHOW statements are show stoppers on server side. While clients can get a SHOW statement as a result set just as any normal SELECT, things are not as such on server side.

On server side, that is, from within MySQL itself, one cannot:


One cannot:


One cannot:

SHOW TABLES INTO OUTFILE '/tmp/my_file.txt';

So it is impossible to get the results with a query; impossible to get the results from a stored routine; impossible to get the results by file reading...

Bwahaha! A hack!

For some SHOW statements, there is a way around this. I've been banging my head against the wall for weeks now on this. Now I have a partial solution: …

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CodeBits - An event of competitive innovation

It was my pleasure and privilege to attend Codebits in 2009. As Roland Bouman says, its talk choice method is based on public voting, and therefore everyone cha have contribute to the schedule.But that is not the main reason for attending this extraordinary event. It is not just a conference. It's an innovation fest. For 1 and 1/2 days, it's a conference, where the speakers are encouraged to bring to their audience the most innovative and inspiring talks. In the afternoon of the second day, the event becomes a competition, where the teams that have registered will have 24 hours to bring a project to completion, and they have to start and finish within the allotted time. The project can be anything, and I have seen quite a lot …

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Gearman for MySQL

If you haven't yet heard about Gearman, it's time to have a look at it. Its distributed client server architecture are a perfect match for today's cloud oriented applications.
When talking about Gearman, much stress is often given on its scalability features, such as map/reduce and distributed loads. But Gearman has also a distinctive advantage in the feature department, because of its design that I like to describe as cooperation of the fittest.

While a traditional application is written entirely in a given language, or it must find ways of integrating multiple languages parts, Gearman encourages easy cooperation between parts written in different languages, eliminating the need …

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Cleaning up Wordpress comment tables

In Montreal with Dups and Kaj, we were looking at a number of technical problems, and each one of you got something valuable from the meeting.
One of Kaj's problems was a collection of Wordpress blogs infested by spam. Kaj has done something already but the situation was critical. Before applying Akismet to his comments, he needed to cleanup the majority of the spam in same easy way.

It is not rocket …

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