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记一次MongoDB性能问题 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...验证这种可能，我搜索了一下MongoDB日志：
shell> grep FileAllocator /path/to/log
[FileAllocator] allocating new datafile ... filling with zeroes...
[FileAllocator] done allocating datafile ... took ... secs
我使用的文件系统是ext4（xfs也不错 ），创建数据文件...
How can I get a count of the total number of digits in a number?
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@Krythic string allocation is the new craze in .NET world.
– nawfal
Dec 9 '16 at 7:16
1
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Why is it bad practice to call System.gc()?
...ly not necessarily true - the Java heap itself grows independently of Java allocations.
As in, the JVM will hold memory (many tens of megabytes) and grow the heap as necessary. It doesn't necessarily return that memory to the system even when you free Java objects; it is perfectly free to hold o...
How to round a number to n decimal places in Java
...ing. I'm surprised Chris Cudmore would even say what he said to be honest. allocating objects is always more expensive than casting primitives and using static methods (Math.round() as opposed to decimalFormat.format()).
– Andi Jay
Jul 10 '12 at 14:35
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java.util.regex - importance of Pattern.compile()?
...r object that is only ever used by one thread at a time in order to reduce allocations.
– AndrewF
Jul 3 '19 at 20:40
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How to Sort a List by a property in the object
...ory you are using is not an issue, this solution avoids unnecessary memory allocation which is EXTREMELY expensive. This option is just as simple codewise and an order of magnitude faster.
– Cdaragorn
Dec 14 '16 at 20:58
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push_back vs emplace_back
...ving does not make s invalid, the move will only steal the internal memory allocation already done in s and leave it in a defaulted state (no sting allocated) which when destructed will be fine as if you had just typed std::string str;
– David
Nov 30 '10 at 0:5...
How to add spacing between UITableViewCell
...Path
{
if (cell.IsMonth)
{
UIImageView *av = [[UIImageView alloc] initWithFrame:CGRectMake(20, 20, 20, 20)];
av.backgroundColor = [UIColor clearColor];
av.opaque = NO;
av.image = [UIImage imageNamed:@"month-bar-bkgd.png"];
UILabel *monthTextLabel = [[U...
Why can I not push_back a unique_ptr into a vector?
... (e.g., when the function returns, in this case). You need to dynamically allocate the object:
std::unique_ptr<int> ptr(new int(1));
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fo...
Should I use Java's String.format() if performance is important?
... follow (average of 5 runs each):
Approach Time(ms) Memory allocated (long)
'+' operator 747 320,504
String.format 16484 373,312
StringBuilder 769 57,344
We can see that String '+' and StringBuilder are practicall...