Questions tagged [performance]
For questions pertaining to the measurement or improvement of code and application efficiency.
performance
102,483
questions
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Why is processing a sorted array faster than processing an unsorted array?
In this C++ code, sorting the data (before the timed region) makes the primary loop ~6x faster:
#include <algorithm>
#include <ctime>
#include <iostream>
int main()
{
// ...
- 501k
4435
votes
54
answers
2.5m
views
Which "href" value should I use for JavaScript links, "#" or "javascript:void(0)"?
The following are two methods of building a link that has the sole purpose of running JavaScript code. Which is better, in terms of functionality, page load speed, validation purposes, etc.?
...
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Why is the Android emulator so slow? How can we speed up the Android emulator?
I have got a 2.67 GHz Celeron processor, and 1.21 GB of RAM on a x86 Windows XP Professional machine.
My understanding is that the Android Emulator should start fairly quickly on such a machine, but ...
3485
votes
25
answers
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What is the difference between call and apply?
What is the difference between using Function.prototype.apply() and Function.prototype.call() to invoke a function?
const func = function() {
alert("Hello world!");
};
func.apply() vs. ...
- 38.4k
3382
votes
12
answers
503k
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Improve INSERT-per-second performance of SQLite
Optimizing SQLite is tricky. Bulk-insert performance of a C application can vary from 85 inserts per second to over 96,000 inserts per second!
Background: We are using SQLite as part of a desktop ...
3029
votes
12
answers
368k
views
Why is "1000000000000000 in range(1000000000000001)" so fast in Python 3?
It is my understanding that the range() function, which is actually an object type in Python 3, generates its contents on the fly, similar to a generator.
This being the case, I would have expected ...
- 44.5k
2994
votes
3
answers
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Why is printing "B" dramatically slower than printing "#"?
I generated two matrices of 1000 x 1000:
First Matrix: O and #.
Second Matrix: O and B.
Using the following code, the first matrix took 8.52 seconds to complete:
Random r = new Random();
for (int i = ...
- 26.9k
2889
votes
7
answers
1.1m
views
How does database indexing work? [closed]
Given that indexing is so important as your data set increases in size, can someone explain how indexing works at a database-agnostic level?
For information on queries to index a field, check out How ...
- 83.7k
2440
votes
11
answers
260k
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Why are elementwise additions much faster in separate loops than in a combined loop?
Suppose a1, b1, c1, and d1 point to heap memory, and my numerical code has the following core loop.
const int n = 100000;
for (int j = 0; j < n; j++) {
a1[j] += b1[j];
c1[j] += d1[j];
}
...
- 25.7k
2122
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41
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How do I measure elapsed time in Python?
I want to measure the time it took to execute a function. I couldn't get timeit to work:
import timeit
start = timeit.timeit()
print("hello")
end = timeit.timeit()
print(end - start)
- 21.3k
2012
votes
19
answers
1.0m
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How to efficiently count the number of keys/properties of an object in JavaScript
What's the fastest way to count the number of keys/properties of an object? Is it possible to do this without iterating over the object? I.e., without doing:
var count = 0;
for (k in myobj) if (myobj....
- 64.7k
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votes
15
answers
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Is < faster than <=?
Is if (a < 901) faster than if (a <= 900)?
Not exactly as in this simple example, but there are slight performance changes on loop complex code. I suppose this has to do something with generated ...
- 15.7k
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How do I profile a Python script?
Project Euler and other coding contests often have a maximum time to run or people boast of how fast their particular solution runs. With Python, sometimes the approaches are somewhat kludgey - i.e., ...
- 48.3k
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7
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Why does changing 0.1f to 0 slow down performance by 10x?
Why does this bit of code,
const float x[16] = { 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,
1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6};
const float z[...
- 14.9k
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11
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Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
I was looking for the fastest way to popcount large arrays of data. I encountered a very weird effect: Changing the loop variable from unsigned to uint64_t made the performance drop by 50% on my PC.
...
- 39.4k