Monthly Archives: February 2020

Stress testing with Raspberry Pi

I have a system – a micro service architecture platform – built on Node.js. It can run on a single computer or distributed. It is a quite small system but quite critical that it works correctly.

Under what circumstances would the system fail to work correctly? How much load can it handle? How does it behave under too heavy load?

Stress testing is difficult, and expensive. Ideally you have plenty of test clients simulating realistic usage. It can be done, but often not easily. A simple and cheap option is to run the system on less resources.

My system used to run perfectly on a Raspberry Pi. The tests work fine. I have also kept the integrationtests working (although there have been timing issues). However, the other day I tried to restore production data to the Raspberry Pi, and it failed to run properly. Problems were

  • High latency and timeouts
  • Heavy swapping
  • Escallating retries, making the situation worse

The last point is particularly interesting. Error handling is designed for stability and recovery, but it risks increasing the total load, making the system even more unstable.

I did make the system work on a RPi again, and in doing so I leant about real problems, and fixed them. It is an interesting excersise in finding problems in systems that don’t work properly, and it is a practical way to “measure first, optimize second”.

Does your system work, with a reasonable amount of production data, on a Raspberry Pi?

Old and new Glenfiddich

I was given an old Glenfiddich miniature. It is probably from the 1960s and it has been stored dark and cold.

I bought a kit with the current Glenfiddich line of standard whiskies and made a little tasting. This is what I find about the old miniature.

The color is more pale, which is reasonable given that it the label says it was 8 years old when bottled, and there is no reason it should get darker being stored in a bottle.

A few minutes in the air made the aroma more pleasant. It was still a light, fruity (almost like white wine) aroma – not very different from the 12 YO.

Both on the nose and in the mouth I found the dominant thing to be “jerusalem artichoke”. I occationally find that in whiskies, never in Glenfiddich before, but sometimes in old whiskies.

All the modern Glenfiddich are partly stored on Sherry casks. I think the miniature was not, and I think that makes it taste a bit different.

I think most people would have prefered the 15/18YO to the miniature. But it is a matter of taste. It had not turned bad. If the difference between the miniature and the 12YO is mostly because of different production methods, or 50 years on a bottle, I can not tell.

I doubt this miniature had been a major success if it was sold. Everything was not better in the past, and storing whisky for half a century on a bottle is hardly a silver bullet to fanstatic whisky. Perhaps it give a taste that is hard to find otherwhise.

Linux on Hades Canyon

About a year ago I got a Hades Canyon NUC for Windows and Gaming. I have been happy enough with it to buy another one for running Linux, Xubuntu.

Basically Xubuntu 19.10 works perfectly on the Hades Canyon NUC. It was all smooth, except:

  • HDMI audio is low quality – for me it is acceptable to use the 3.5mm plug instead, but if you want HDMI audio this is bad for you

I think with NUCs Intel has managed to produce computers that are very good, and I don’t really see myself buying any other desktop computers. Why are there no AMD computers in this segment?

Keeping open Whisky bottles

So, you open a bottle of whisky, drink a little now and then, and years later you wonder if it still tastes the same?

Here are my empiric notes:

Deanston 12: One of the bottles is opened since perhaps 2 years, and has been almost empty for months. Head to head, initially, I slightly prefer the old bottle on the nose. But tasting, going back and forth, it is the same whisky.

Famous Grouse: I have a plastic bottle of Famous Grouse with very little left in it. It has probably been open for 10 years. It actually tastes significantly worse – more burning and chemical – than a fresh bottle.

Lagavulin 1984: This bottle has been opened for almost 20 years and there is not much left. When it was newly opened I compared it to a standard Lagavulin 16. Then my experience was that 1984 and 16YO was very similar, but 1984 was a little extra. Today I opened a new Lagavulin 16 and compared to the 1984. The 1984 is much softer, I guess the ABV is lower, and both aroma and taste has a clear jerusalem artichoke element to it. My conclusion is that 1984 is definitely changed, not necessarily for the better, but it is not much worse either. It is still enjoyable (some people would probably prefer it for being softer), it is still a Lagavulin, but it is not exactly the same.

Simple Vegetable Oil Lamp

WARNING: The lamp prototypes suggested below may not be safe for general use: especially not around children, left unattended, or close to anything flamable.

Oil Lamps

I got a beautiful Oil lamp that I use much.

Oil Lamp

This lamp uses Lamp Oil (kerosene, paraffin oil). When I bought that I was a little chocked with two thing:

  1. The price (compared to vegetable oil)
  2. How seriously poisonous it is (to the point I dont like to handle it, and I wonder if I want it at home at all)

However this “real” Oil lamp does not run well on vegetable oil (I have tried canola oil). It runs for a while but I think the problem is that the viscosity is too high so the oil does not flow properly upwards through the wick as required.

Vegetable Oil

I can buy canola oil for 25% of the price of lamp oil. And it is obviously not dangerous (since it is for cooking). However it is thicker and has a higher flash point. It is also supposed to not burn cleanly (leaving smoke and smell). So I was curious if I could design a simple practical and not too ugly oil lamp for simple (unused) cooking oil.

Skipping the failed designs here are the ones that kind of work.

A can lamp

What you see in the picture are five components:

  1. a metal can
  2. canola oil
  3. a few candlewicks
  4. a metal washer (the flat metal ring with a small hole in it)
  5. a metal “bridge”

placed inside a fireplace. This burns well: no smoke, no smell, burns for hours. I have read that vegetable oil consumes the wick faster than lamp oil. Perhaps that is true, but nevertheless the wick lasts much longer than it would have in a normal candle.

A little bottle lamp

How about moving the metal washer with the wick to a small bottle?

This is a very simple design and as you can see in the (somewhat unsharp) picture it burns nicely. But it only burns nicely for about 60min, and then it burns barely for another 60 minutes and then it dies.

Only the canola oil in the bottleneck is consumed. After that it appears the height difference between the oil level and the washer/fire prevents the oil from ascending the wick (fast enough).

A used candle jar

I tried filling an old candle jar with about 1cm of canola oil, and used a wick and a metal thing for this result.

This burns nicely! The sides of the candle jar does not get very hot, and the bottom of and the oil remains quite cool. The metal thing from a hardware store is obviously designed for another use.

The good thing with this design is that it is simple (jar+metal thing+wick) and that not so much oil goes into the lamp. You can easily reuse pretty candle jars that are already designed for the purpose.

Spirit Burner

I would not guess that most spirit burners (or oil lamps) work well. But SPIRI-1 from Böhm Stirling-Technik works perfectly with canola oil. The good thing is that it is (roughly) the size of a tealight so you could replace your disposable tealights. The bad thing is that it is quite expensive.

Conclusions

First I think vegetable (canola) oil is underestimated for decorative light at home. However I can see that tealights can be sold and managed in a safe way and are easier to use.

It often requires two matches to light the canola, because the flash point is very high. However I think the high flashpoint is also good for safety.

Cheap candles and tealights are made of petroleum and they don’t necessarily burn cleanly without leaving unhealthy particles in the air. I can not guarantee that the canola oil also does not leave any particles in the air, but the oil itself is not toxic at all.