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When mobile users feel they don't like how their apps perform after the first trial, some 75% of them won't launch the app again. That's the metric cited by engineers and marketers at HP Software, who note that this first wave of mobile apps brought forth by the iPhone has resulted in a glut of programs that make even the best performing mobile hardware into a pocket full of silicon cement.

This morning, HP begins a repurposing of the performance testing tools for websites that it gained through the Mercury Interactive acquisition of 2006, for the mobile apps era. It's unveiling what it calls "LoadRunner-in-the-Cloud," complete with hyphens. It will act as an off-premise testing platform for mobile apps that are deployed as services, simulating the activity generated by thousands of users simultaneously to gauge the resilience of servers and resources. This way, you might not have to disappoint three-fourths of them to learn how well your service holds up.

Legendary computer scientist Donald Knuth wrote that "premature optimization is the root of all evil," referring to the amount of time and effort programmers spend optimizing non-critical elements of their applications.

On the other hand, as pointed out in this blog post by Metamarket CTO Mike Driscoll on the company's migration to Node.js, it's better to swap out critical infrastructure early in a startup's life.

So, when you're building an application - when do you start thinking about scalability?

Last week we told you about how Twitter is migrating its search stack from Ruby to Java. But Twitter is also known for being an early adopter of Scala. This presentation by Marius Eriksen at the Commercial Users of Funtional Programming 2010 conference explains how Twitter uses Scala to scale.

A few people from Facebook's database teams (yes, plural) recently gave a MySQL Tech Talk at Facebook headquarters about how Facebook uses MySQL to process 13 million queries per second. Former Facebook CTO and Quora founded Adam D'Angelo has said that Facebook is "stuck" with PHP and MySQL for legacy reasons, but it sure sounds the Facebook team is making the best of it. Video and notes after the jump.

It should be any entrepreneur's dream come true. But for some startups, a sudden, overnight explosion in growth can nearly bring the operation to its knees.

Such was the recent experience of Blank Label, a Web-based company that sells custom-made, user-designed dress shirts for men. After launching in October 2009, Blank Label enjoyed some modest initial success, selling a few hundred shirts in the first few months of business.

Earlier this month, Ben Horowitz of Andreessen Horowitz brought up an interesting topic surrounding the hiring and firing of executives at startups. While talking with a pair of his friends - one a VC and the other a startup CEO - the CEO asked if he should get rid of an executive as the company grows larger because he lacks experience leading a larger company. As Horowitz explains in his post "The Scale Anticipation Fallacy," he believes passing judgement based on how an executive might perform in the future is ludicrous.

There is a significant risk and reward that comes with developing products that leverage third-party application programming interfaces, or APIs. Twitter has used its API to let others spread the word for them; applications like Tweetie and TweetDeck help Twitter reach a broader audience on a variety of devices while making money for themselves. However, downtime for a service offering their API to developers means downtime for every service that relies on it for its API data. In the case of Facebook application developers, continuing reliability issues with the platform have become a cause for concern.

Editor's note: we offer our long-term sponsors the opportunity to write 'Sponsor Posts' and tell their story. These posts are clearly marked as written by sponsors, but we also want them to be useful and interesting to our readers. We hope you like the posts and we encourage you to support our sponsors by trying out their products. This one is by Hakia, one of the participants in the recent 2009 Semantic Technology Conference.

Participants in the 2009 Semantic Technology Conference walked away considering fundamental questions about what is and isn't semantic technology. The relevance of this post's title will hopefully become clear by the end to those of you mischievous readers who may have stumbled upon it with other ideas. The conference was a great and well-organized affair in San Jose, California. One of the highlights was the Semantic Search Keynote panel, with all of the major players on stage (Ask, Bing, Google, Hakia, TrueKnowledge, and Yahoo!), as seen in the picture below.

Once upon a time, whenever anyone asked, "But are there any big applications built on Rails?" The answer was usually, 43Things, anything from 37Signals, or Odeo. But over the past year, there's no doubt that if there is a poster child for Rails, it is now Twitter. With such notorious bouts of downtime, a worse poster child Rails could not possibly hope for. But is Twitter even the largest application out there running on Rails? Does it even matter?