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Category: Erklärbär

Using MySQL Partitions (a Python example)

Today somebody had a problem with expiring a large table (a Serendipity Blog table).

In MySQL InnoDB, tables are physically ordered by primary key (InnoDB data is a B+ tree, a balanced tree where the data pages are the leaves of the tree). If you are expiring old data from such a log table, you are deleting from the left hand side of the tree, and since it is a balanced tree, that triggers a lot of rebalancing – hence it is very slow.

If you rename the old table and INSERT … SELECT the data you want to keep back into the original table, that can be faster. But if the data you want to keep is larger than memory, the indexing of the data will still be slow.

A nice way to handle log tables are partitions. Here is an example. It’s not very cleaned up, but it works on my system.

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New Technology vs Planned Obsolescence

based on an old Google plus article from 2015:

What you observe as Planned Obsolescence is often the natural outcome of fast product cycles that are necessary for any new technology.

When a new thing arrives in the market, it is often barely viable, a minimum viable product. We are remembering the iPhone 1 as revolutionary, but we chose to forget about is slowness, its clunkyness and the very limited feature set it had. And those of us having purchased a car with built-in satnav now have to deal with a car radio where you have to choose between listening to a CD or putting in the outdated CD-ROM with navigation data – and then wait for a minute until you get the route.

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A modest solution to a simple problem: Filter on X-Trigger headers in Gmail

I have a very simple problem. My Gmail is receiving a mail with an X-Trigger header and I need to filter these messages (mark them as Archived, as Read an label them into the “filtered” category).

Here is a sample:

$ cat t
X-Trigger: test
Subject: a test
From: kris@koehntopp.de (Kristian Koehntopp)
To: kristian.koehntopp@booking.com

Testing
$ mutt -H t
...

Now, generating filters in Gmail is very easy for various capabilities, but for some reason filters on arbitray header lines are not possible.

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Rolling out patches and changes, often and fast

Fefe had a short pointer to an article Patching is Hard. It is, but you can make it a lot easier by doing a few things right.  I did s small writeup (in German) to explain this, which Fefe posted.

I do have an older talk on this, titled “8 rollouts a day” (more like 30 these days). There are slides and a recording. The Devops talk “Go away or I will replace you with a little shell script” addresses it, too, but from a different angle (slides, recording).

Here is the english version of the writeup:

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Handling Wannacrypt – a few words about technical debt

So Microsoft had a bug in their systems. Many of their sytems. For many years. That happens. People write code. These people write bugs

Microsoft over the years has become decently good with fixing bugs and rolling out upgrades, quickly. That’s apparently important, because we all are not good enough at not writing bugs. So if we cannot prevent them, we need to be able to fix them and then bring these fixes to the people. All of them.

The NSA found a bug. They called it ETERNALBLUE and they have been using it for many years to compromise systems.

In order to be able to continue doing that they kept the bug secret. That did not work. The bug is now MS17-010 or a whole list of CVE-entries.

The NSA told MS about the bug when they learned that it had leaked, but not before. Microsoft patched the bug in March 2017, even for systems as old as Windows XP (which lost all support in 2014), but many people did not install the patch.

The result is “the largest cyberattack in the world”.

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WordPressing…

This blog is running a WordPress, using Ubuntu, Apache and MySQL. So it’s a very basic installation.

I made all this with a tiny Scaleway VM and Ansible. My Goal has been to install this thing without actually having to log into the VM (“Look Mom, no hands!”). Of course, I have been logging into the VM, but that’s mostly for checking things are going well.

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Containers 101

It is helpful to remember that containers are just normal Unix processes with two special tricks.

Normal Unix Processes

Unix starts processes by performing a fork() system call to create a new child process. The child process still contains the same program as the parent process, so the parent processes program still has control over the child. It usually performs a number of operations within the context of the new child, preparing the environment for the new program, from within.

PID 17 forks, and creates a new process with PID 18. This process executes a copy of the original program.

Then, after the environment is complete, the parent program within the child processes context replaces itself by calling execve(). This system call unloads the current program in a process and reuses the process to load a new program into it.

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