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Comment by grokys | Hacker News Reader

Yes, but it's unlikely that someone asking "is it faster to concatenate strings in C# using the + operator or StringBuilder" on StackOverflow is someone that is writing a low-level database engine like SQLite. In my (totally anecdotal) experience the people who are more concerned about performance are beginners, because that is something that they can grasp, and this is where the "don't prematurely optimize" people are coming from. Obviously someone who is writing a low-level database engine knows that performance matters, and likewise, is likely to be running benchmarks rather than asking vague questions on SO.

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Indeed. However, keep in mind that as this beginner "ramps up" to the knowledge level of someone who is working on a SQL database he will need a source to find out where costs lie. He's done some profiling, finds an expensive method with massive amounts of string concats, heads to Google and all he can find is "don't prematurely optimize."

You can supplement an answer with "don't prematurely optimize," but the presumption that premature optimization is occurring is a premature assumption.

He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever. ~ Chinese Proverb

I would work with beginners that are not fools, than experts who are.

Nope, if he got to that level, he'll know that the only way to really know it is testing.

He may still ask why one is slower than the other (if it is, I don't know that), but that's a completely different question that in most contexts will get a nice answer.

Suppose, for a moment, that our hero is seeing this situation for the first time and doesn't know what the alternatives are.

Tests that don't cover the best option can't possibly identify the best option. So if you want to do a really good test, going somewhere to ask, "What else should I try?" is hardly an asinine course of action. On the contrary, if our hero is new to this stuff, or is new to the platform in question, or anything like that, then asking others for advice should probably qualify as due diligence.

> He's done some profiling

In my experience on Stack Overflow, the people getting hit with accusations of "premature optimization" have not gone this far.

And that's decent advice in response to the "is it faster to concatenate strings in C# using the + operator or StringBuilder" questions. But I've also asked Stack Overflow questions that drowned under a tsunami of premature optimization tut-tutting from people who I suspect didn't even fully understand the question, and then sighed and proceeded to take a couple days to figure it out myself and improve application performance in a critical section by 50%. Which is fine, but once upon a time I thought Stack Overflow might be a resource where people might occasionally save me a bunch of time by saying, "Hey, don't waste your time, I've been there and it's a blind alley."

I think part of what's going on there is that SO's gamification can create some kind of perverse incentives for answerers. If you want to get the upvotes, you have two good courses of action: You can either already have 5 digits' worth of karma, or you can answer first. The first option isn't available to the vast majority of SO users, so most go with the latter one. This drives down the quality of answers. It also creates perverse incentives for behaviors such as users getting in a quick low-quality response that's just good enough to get a few upvotes from people who already understand what you're talking about, and then (maybe) following it up with an edit that provides a high-quality response that would be useful to the asker.

It helps to preempt the typical response. If I post a question that's "premature optimization bait" I end it with:

> I'm optimizing this due to profiler results.

You'd be surprised how many people still question whether I'm prematurely optimizing in the comments, but the actual answers tend to be more helpful.

Have you tried something more along the lines of:

I'm trying to do X.

Currently, I'm using Y mechanism, and it produces correct results.

However, the performance sucks -- profiling shows me this is a big time sink in my program. So... (actual question.)

It may help with kneejerk "premature optimization" if the profiler results are mentioned before the request about how to optimize (at least, it should to the extent that the problem is people stopping reading because they see the optimization request so that they never read the comment about profiler results.)

> But I've also asked Stack Overflow questions that drowned under a tsunami of premature optimization tut-tutting from people who I suspect didn't even fully understand the question, and then sighed and proceeded to take a couple days to figure it out myself and improve application performance in a critical section by 50%.

Me too. It's infuriating how presumptuous people can be.

Here is someone insisting to me over and over that virtual function call overhead is not measurable: http://stackoverflow.com/a/16603295/77070

Here is someone telling me that my attempts to avoid a virtual function call "definitely fall under the category of premature optimization": http://stackoverflow.com/a/5100072/77070

It's interesting to me that people will shout "premature optimization" before they have any idea what you are doing or how long you have worked on this problem before trying to optimize.

I'm also deeply skeptical of the pre-canned response that people should always profile - in the spirit that it's hopeless to optimize without a profiler.

In my experience, profilers are really low-level tools that often highlight the wrong problems, aren't very good at telling you where the optimization opportunities are, and tend to encourage microoptimization.

It's not that profilers are bad, it's that I get the feeling the people parroting this advice have no idea what they're talking about, and somehow believe that a profiler is "the solution", when profilers are neither necessary nor (most problematically) sufficient to fix most performance problems.

For me, profilers are most useful for

1. quickly seeing which high level functions or methods take the longest time, 2. which methods are called a lot.

Even 2. can be of marginal use. A lot of times, it's not surprising a method is called a lot, and not clear whether those calls are indicative of a performance problem. There are times, though, where a method is called a lot more than you expected, in which case it might be the clue to solving the performance problem.

For 1., it's usually click down through the call stack for the most expensive top level method, while there is still a single method taking up a good fraction of the overall time.

Hopefully the stopping point will still be a method you wrote, and not a library call. If it's your code, you likely have the ability to fix the performance problem by changing your code. If it's a library call, you might need to be a little more creative, in finding an alternative approach, or better understanding what that library call is doing under the hood.

So for me, the profiler just tells me I'm looking at the right general part of the code when trying to improve performance, and that's about it.

FWIW, both 1 and 2 can still lead you in the wrong direction sometimes. For example, if you're working in a garbage-collected language most profilers (that I've used, anyway) won't give you good insight into how much time you're wasting on excessive GC load because you're creating too $#@$% many unnecessary objects (see: boxing), or creating objects with just about exactly the wrong life span. If you're working on parallel code, many profilers are darn near useless for figuring out how much time you're losing to blocking on synchronization.

I just replaced a SQL view that was performing 24,000 reads with a procedure that performs 45 reads. Yes, it's a little different to use, but overall don't listen to the premature optimization people.

I could wait until the data in those tables grows to a crazy size and the reads are out of control (and spilling to disk) or I could just fix it now. Hmmm...

And then you post your own solution for others who might stumble upon it and 15 minutes later the entire thread is deleted by a mod for "this is a discussion thread and doesn't fit the Stack Overflow Modus Operandi"

> If you want to get the upvotes, you have two good courses of action: You can either already have 5 digits' worth of karma, or you can answer first.

How does having karma help you get more upvotes on a brand new answer?

Answers that already have upvotes get more views, and are therefore more likely to get even more upvotes. But that's distinct from a user's reputation score.

To be fair, I once fixed a java application that completely crashed due to using string concatenation for data export, rather than a StringBuffer. It does matter sometimes even in workaday applications.

It's not a completely useless question. I wrote an API data validation gem for Ruby that needs to be as unobtrusive as possible, so it needs to be fast. I found that building strings by interpolation (e.g. "#{str1}#{str2}") is quite a bit faster than addition (e.g. str1 + str2).

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