Eventually consistent

Sample Facebook update illustrating the problem

Facebooks’ eventually consistent database has been under real strain lately. It’s a great example of the difference between social media and the web 2.0 style architectures, and a banking application. In this example, facebook has notified me three separate ways that a conversation had been updated. Yet almost 20-seconds after the first notification, the data I can see hasn’t been updated. The facebook comment made by Mike in the top-right, should be appended to the bottom of the pop-out window.

Now, imagine this was your bank account. A transaction comes in that debits $10,000 from your account. Then a query comes in that shows the $10,000 is still in your account, another transaction is then initiated that deducts $10,000 from your account. What got debited, and if you only had $15,000 in your account, how much do you have now?

And that’s a great example of the difference between eventually consistent and ACID based transaction-based systems. Many but not all IT Professionals understand this. Make sure yours does. In this case it could be the backend database consistency, ie there are multiple copies and they don’t match, or there could be multiple backend copies and the copy in the browser cache, does or doesn’t match. Either way “Houston, we have a problem”.

The implications of “Mastered for iTunes”

Picture of a sound meterNPR has an interesting blog entry on “What ‘Mastered For iTunes’ Really Means”. I hadn’t spotted this since I’ve been a life long Apple avoider. It’s not that I think Apple has bad products, it’s just they always, always look for a way to lock users into their systems. I’ve felt for a long time that the music industry would eventually find a way to strike back at MP3. In this case it makes perfect sense. Pay particular attenion to the last two paragraphs.

http://www.npr.org/blogs/therecord/2012/02/24/147379760/what-mastered-for-itunes-really-means

Testing live blog via gprs

++ Check the date out on this entry! It was originally posted from the original smart phone to my livejournal account on that date. I’m considering importing my whole livejournal account here… Thoughts? It was mostly travelling and triathlon posts. ++

So, still in setup mode and exploring how livejournal works. This entry came live from my Palm Tungsten W.

Later, I edited this entry and added a link to the tri club I’m currently the chairman of, Tri-Force