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Category: Computer Science

Swap and Memory Pressure: How Developers think to how Operations people think

There is a very useful and interesting article by Chris Down: “In defence of swap: common misconceptions“. Chris explains what Swap is, and how it provides a backing store of anonymous pages as opposed to the actual code files, which provide backing store for file based pages.

I have no problem with the information and background knowledge he provides. This is correct and useful stuff, and I even learned a thing about what cgroups can do for me.

I do have a problem with some attitudes here. They are coming from a developers or desktop perspective, and they are not useful in a data center. At least not in mine. :-)

Chris writes:

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Knock, Knock

What does your Mac do on Startup? Knockknock knows.

It’s not properly updated for current versions of MacOS, but it is still useful. “git clone https://github.com/synack/knockknock” and “/usr/bin/python knockknock.py” is sufficient to test.

TOTAL ITEMS FOUND: 44

That’s quite a bit. Apparently, I am starting

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Conway’s Law

Melvin Conway is a compiler developer and systems designer, who is well known for the eponymous Conway’s Law. Various phrasings exist of that, and one popular is

Organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations.

The original paper and an introductory paragraph can be found on his website. It’s worth reading, because there are more useful insights to be found in the original writeup.

So what does this even mean? Can you give examples from your current or previous work environments?

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To France…

A few days ago, a few of “us” have been to france. On a cold November morning in a brand new data center hall, we had a look at some Version 1 OCP racks, and a very nice conversation with a bunch of friendly people interested in getting the foundation going.

A OCP Version 1 rack, with three power zones. You can see the centralized power supplies at the bottom of each of the zones.

See Open Rack Specs and Designs, the Open Rack Standard 1.2 Spec and Facebook Open Rack V1 Specification. There is also the Facebook V1 Power Shelf Specification.

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Redfish, Rack Scale Design and Remote Anything

The Intel RSD Platform Guide (PDF) is the one document you should skim front to back, it’s really useful.

Back in the bad old time, server computers had a proprietary  management controller (BMC), for example HP iLO or Dell iDRAC. These varied widely in capabilities, and worse, in data structures presented to the management software controlling the data center.

A lot of standards came, and failed, until pressure from certain customers with a lot of machines, everybody kind of centered around Redfish. All modern servers, no matter who makes them, understand Redfish.

But Redfish does not stop at the server, nor is it the whole story. It is cross linked to Rack Scale Design (RSD), which is an initiative lead by Intel and joined by many vendors to build composable hardware.

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Kissing “sex enum(‘m’, ‘f’) not null” goodbye.

The german constitutional court just created a major database upgrade problem, for good: They mandated a positively stated third gender.

That basically makes this code illegal:

CREATE TABLE t (
...
  sex enum('m', 'f') NOT NULL,
...
);

as this would force a decision between the only alternatives male and female. Also, code like

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Power budgets for computing resources – portable and stationary

A cellphone or tablet is a fanless device. So is the 12″ Macbook. That means you can do whatever is possible at any point in time within a TDP of approximately 5W.

Here is the power consumption of my cellphone over a 12h period. The scale on the left is mW, down is discharge, up is recharge (plugged in). It’s basically limited to 5W, and that only for short periods of time.

Cellphone power over time. Green bar = plugged in. Yellow bar = Screen on.

These devices also have batteries, and when they are running on batteries, they need to be sleeping most of the time and have their display off. Whenever they are not dark and/or sleeping, they drain the battery, fast.

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Every Conversation ever held

So, let’s do this again, but this time cleanly. In a Facebook Post, Michael Seemann has been explaining why the Facebook App does not listen to every word you ever say, all of the time.

He is right. A telephone is a device with limited power supply, limited cooling and limited, metered connectivity. It has an operating system that monitors and manages these critical resources, hard. You can’t listen to things all of the time and expect not to be noticed. Like, “the battery is empty and my LTE budget is gone” noticed.

Other devices, an Alexa, a Sonos One or a Google Home, are on cabled power and unmetered Wifi. The could theoretically get away with listening all of the time.

So how much data is that? Let’s do the math.

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Unicode is over and it dies over Emoji

In 1982, Scott Fahlmann invented the use of :-) and :-( for marking up emotions or semantic context in written online communication. That was a great idea.

The :-) is just a symbol for an emotion. It is specifically not a human face, it does not have a hair color, eye color, skin color or other human attributes. It is universal.

Then some cellphone maker turned that into ☺︎, anthropomorphising it. Come as it must, we soon get color, and it turns into 🙂. That Simpsons yellow was read by some as white and non-inclusive, and here is where things start to break down.

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