unix domain socket(简称unix socket) 与TCP/IP sockets通信的 区别
unix domain socket(简称unix socket) 通信，平均需要6毫秒，TCP/IP sockets通信平均需要6毫秒，即在同一台服务器上，使用unix domain socket通信比TCP/IP sockets更快。
下面是一些英文资料有详细深入分析2种通信方式的区别。
Unix Domain Sockets are generally faster than TCP sockets over the loopback interface. Generally Unix Domain Sockets have on average 2 microseconds latency whereas TCP sockets 6 microseconds.
A UNIX socket is an inter-process communication mechanism that allows bidirectional data exchange between processes running on the same machine.
IP sockets (especially TCP/IP sockets) are a mechanism allowing communication between processes over the network. In some cases, you can use TCP/IP sockets to talk with processes running on the same computer (by using the loopback interface).
UNIX domain sockets know that they’re executing on the same system, so they can avoid some checks and operations (like routing); which makes them faster and lighter than IP sockets. So if you plan to communicate with processes on the same host, this is a better option than IP sockets.
Edit: As per Nils Toedtmann’s comment: UNIX domain sockets are subject to file system permissions, while TCP sockets can be controlled only on the packet filter level.
What’s the difference between Unix socket and TCP/IP socket?
A TCP/IP socket is used for communication across TCP/IP networks. A connected TCP socket is identified by the combination of local IP, local port, remote IP and remote port. A listening TCP socket is identified by local port and possibly local IP. AIUI at least on linux TCP/IP sockets always result in the generation and decoding of TCP/IP packets, even if the client and server are on the same machine.
A unix domain socket (sometimes shortened to unix socket) on the other hand operates on a single machine. Listening sockets live in the filesystem hierarchy and access to them can be controlled by filesystem permissions.【wyq：example，php-fpm use unix socket ，can configure the user and group who connect to php-fpm process 】
Furthermore a process accepting a connection on a Unix socket can determine the user ID of the process that connects. This can avoid the need for an authentication step. Rather than generating a password for your database server and including a copy of it in your webapp’s code you can just tell the database server that the user running the webapp has access to the corresponding user account in the database.
You can list your own machine local unix sockets with the following command:
netstat -a -p --unix
The Unix socket implementation can send and receive more than twice the number of messages, over the course of a second, when compared to the IP one. During multiple runs, this proportion is consistent, varying around 10% for more or less on both of them. Now that we figured their performance differences, let’s find out why Unix sockets are so much faster.
It’s important to notice that both IP and Unix socket implementations are using TCP (socket.SOCK_STREAM), so the answer isn’t related to how TCP performs in comparison to another transport protocol like UDP, for instance (see update 1). What happens is that when Unix sockets are used, the entire IP stack from the operating system will be bypassed. There will be no headers being added, checksums being calculated (see update 2), encapsulation and decapsulation of packets being done nor routing being performed. Although those tasks are performed really fast by the OS, there is still a visible difference when doing benchmarks like this one.
There’s so much room for real-world comparisons besides this synthetic measurement demonstrated here. What will be the throughput differences when a reverse proxy like nginx is communicating to a Gunicorn backend server using IP or Unix sockets? Will it impact on latency as well? What about transfering big chunks of data, like huge binary files, instead of small messages? Can Unix sockets be used to avoid Docker network overhead when forwarding ports from the host to a container?
