Senior LevelREST APIs & Web Services
How does the sendfile() system call enable Zero-Copy file streaming in web servers?
❓ Interview Prompt: Explain Zero-Copy file transfer, traditional buffer copy overhead (Disk $\rightarrow$ Kernel $\rightarrow$ User space $\rightarrow$ Socket), `sendfile()` system call, and CPU savings.
Traditional file downloading requires copying data back and forth between kernel space and user space across 4 context switches:
Traditional 4-Copy Overhead:
Disk $\rightarrow$ OS Kernel Read Buffer $\rightarrow$ User Space Application Buffer $\rightarrow$ OS Kernel Socket Buffer $\rightarrow$ NIC Hardware.
'sendfile()' Zero-Copy Optimization:
The 'sendfile()' system call transfers data entirely inside OS kernel space directly from disk buffer to socket buffer:
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0 User-Space Copies and 0 User-Space Memory Allocations!
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Reduces CPU usage by 80% and maximizes network throughput for file downloads.
Code Implementation Example
c
// C System Call: sendfile(out_fd, in_fd, offset, count)
// Transfers file descriptor data directly in kernel space without user-space buffer copies!
ssize_t bytes_sent = sendfile(socket_fd, file_fd, &offset, file_size);💡Zero-Copy file transfer using C sendfile system call.
🎯 Interview Key Takeaway
Use Zero-Copy sendfile() system calls in web servers to stream static files directly inside kernel memory without CPU buffer copy overhead.
#sendfile#Zero-Copy#Kernel#Performance#Senior
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