It depends. See the MySQL Performance Blog post on this subject: To SQL_CALC_FOUND_ROWS or not to SQL_CALC_FOUND_ROWS? Just a quick summary: Peter says that it depends on your indexes and other factors. Many of the comments to the post seem to say that SQL_CALC_FOUND_ROWS is almost always slower – sometimes up to 10x slower – … Read more
This GHC Trac page also explains the passes fairly well. This page explains the optimization ordering, though, like the majority of the Trac Wiki, it is out of date. For specifics, the best thing to do is probably to look at how a specific program is compiled. The best way to see which optimizations are … Read more
Yes – absolutely. Looking up a class via reflection is, by magnitude, more expensive. Quoting Java’s documentation on reflection: Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which … Read more
As a general rule, most if not all Intel CPUs assume forward branches are not taken the first time they see them. See Godbolt’s work. After that, the branch goes into a branch prediction cache, and past behavior is used to inform future branch prediction. So in a tight loop, the effect of misordering is … Read more
This is a pure guess, and I haven’t figured out an easy way to check whether it is right, but I have a theory for you. I tried your code and get the same of results, without_else() is repeatedly slightly slower than with_else(): >>> T(lambda : without_else()).repeat() [0.42015745017874906, 0.3188967452567226, 0.31984281521812363] >>> T(lambda : with_else()).repeat() [0.36009842032996175, … Read more
I’m going to go against the general wisdom here that std::copy will have a slight, almost imperceptible performance loss. I just did a test and found that to be untrue: I did notice a performance difference. However, the winner was std::copy. I wrote a C++ SHA-2 implementation. In my test, I hash 5 strings using … Read more
Yes, window.onfocus and window.onblur should work for your scenario: http://www.thefutureoftheweb.com/blog/detect-browser-window-focus
The difference between parseFloat and Number parseFloat/parseInt is for parsing a string, while Number/+ is for coercing a value to a number. They behave differently. But first let’s look at where they behave the same: parseFloat(‘3’); // => 3 Number(‘3’); // => 3 parseFloat(‘1.501’); // => 1.501 Number(‘1.501’); // => 1.501 parseFloat(‘1e10’); // => 10000000000 … Read more
I needed to know this for sure, so I benchmarked both methods. I consistenly found IN to be much faster than using OR. Do not believe people who give their “opinion”, science is all about testing and evidence. I ran a loop of 1000x the equivalent queries (for consistency, I used sql_no_cache): IN: 2.34969592094s OR: … Read more
It is a very easy-to-use method in C++11. You have to use std::chrono::high_resolution_clock from <chrono> header. Use it like so: #include <chrono> /* Only needed for the sake of this example. */ #include <iostream> #include <thread> void long_operation() { /* Simulating a long, heavy operation. */ using namespace std::chrono_literals; std::this_thread::sleep_for(150ms); } int main() { using … Read more