12,859 questions
27507
votes
25
answers
2.0m
views
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()
{
// ...
- 506k
986
votes
24
answers
563k
views
how do *you* calculate/approximate Big O?
Most people with a degree in CS know what Big O stands for.
It helps us to measure how well an algorithm scales.
How do you calculate or approximate the complexity of your algorithms?
- 18.4k
1754
votes
34
answers
949k
views
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., ...
- 49.5k
276
votes
9
answers
107k
views
Why JSF calls getters multiple times
Let's say I specify an outputText component like this:
<h:outputText value="#{ManagedBean.someProperty}"/>
If I print a log message when the getter for someProperty is called and load the page, ...
- 4,293
644
votes
34
answers
95k
views
Performance optimization strategies of last resort [closed]
There are plenty of performance questions on this site already, but it occurs to me that almost all are very problem-specific and fairly narrow. And almost all repeat the advice to avoid premature ...
193
votes
1
answer
95k
views
What is the best way to set a register to zero in x86 assembly: xor, mov or and?
All the following instructions do the same thing: set %eax to zero. Which way is optimal (requiring fewest machine cycles)?
xorl %eax, %eax
mov $0, %eax
andl $0, %eax
- 2,315
1468
votes
16
answers
1.1m
views
String formatting: % vs. .format vs. f-string literal
There are various string formatting methods:
Python <2.6: "Hello %s" % name
Python 2.6+: "Hello {}".format(name) (uses str.format)
Python 3.6+: f"{name}" (uses f-...
- 17.9k
244
votes
5
answers
70k
views
When should I (not) want to use pandas apply() in my code?
I have seen many answers posted to questions on Stack Overflow involving the use of the Pandas method apply. I have also seen users commenting under them saying that "apply is slow, and should be ...
- 406k
4459
votes
56
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.?
...
333
votes
4
answers
117k
views
What makes a SQL statement sargable?
By definition (at least from what I've seen) sargable means that a query is capable of having the query engine optimize the execution plan that the query uses. I've tried looking up the answers, but ...
- 20.6k
102
votes
3
answers
17k
views
Why is the loop instruction slow? Couldn't Intel have implemented it efficiently?
LOOP (Intel ref manual entry)
decrements ecx / rcx, and then jumps if non-zero. It's slow, but couldn't Intel have cheaply made it fast? dec/jnz already macro-fuses into a single uop on Sandybridge-...
- 378k
1127
votes
20
answers
520k
views
StringBuilder vs String concatenation in toString() in Java
Given the 2 toString() implementations below, which one is preferred:
public String toString(){
return "{a:"+ a + ", b:" + b + ", c: " + c +"}";
}
or
public String toString(){
StringBuilder ...
- 18.9k
392
votes
13
answers
541k
views
How do I obtain a Query Execution Plan in SQL Server?
In Microsoft SQL Server how can I get a query execution plan for a query / stored procedure?
- 87.3k
16
votes
1
answer
4k
views
How to describe performance issue in relational database?
I have a query running in a relational database that doesn't fulfill the expectation of the users.
What information should I provide and what should I avoid, so that I can receive an effective help ...
- 21.3k
3568
votes
78
answers
1.2m
views
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 ...