英文:
Go: Seek+Write vs WriteAt performance
问题
我刚开始学习Go的文件系统操作。似乎至少有两种方法可以进行随机文件写入：
// 1. 首先设置偏移量，然后写入数据
f.Seek(offset, whence)
f.Write(data)
// 2. 一步完成按偏移量写入
f.WriteAt(data, offset)
所有三个函数（Seek，Write，WriteAt）都是使用不同的系统调用实现的：在Unix系统上，Write是通过syscall.Write实现的，而WriteAt内部使用了syscall.Pwrite。
由于Seek+Write执行了两个系统调用，而WriteAt只需要一个系统调用，所以为了更好的性能，第二种方法是否更好？
英文:
I've just started to study Go's filesystem operations. It seems like there are at least two ways to perform random file writes:
// 1. First set the offset, then write data
f.Seek(offset, whence)
f.Write(data)
// 2. Write by offset in one step
f.WriteAt(data, offset)
All of three functions (Seek, Write, WriteAt) are implemented with the use of different syscalls: on Unix systems Write is implemented via syscall.Write and WriteAt has syscall.Pwrite inside.
Since Seek+Write perform two syscalls, whereas WriteAt requires only one syscall, should the second method be preferred for the sake of better performance?
答案1
得分: 2
seek()+read()和seek()+write()都是一对系统调用，而pread()和pwrite()是单个系统调用。较少的系统调用意味着更高的效率。
你可以选择使用WriteAt。
英文:
seek()+read() and seek() + write() are both a pair of sys-calls while pread() and pwrite() are single sys-calls. Less sys-calls - more efficiency.
You can definitly go for the WriteAt
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