How many socket connections possible

Question

Has anyone an idea how many tcp-socket connections are possible on a modern standard root server   There is in general less traffic on each connection  but all the connections have to be up all the time    EDIT  We will use a Linux Server

User · Answer

On Linux you should be looking at using epoll for async I/O. It might also be worth fine-tuning socket-buffers to not waste too much kernel space per connection.

I would guess that you should be able to reach 100k connections on a reasonable machine.

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This depends not only on the operating system in question  but also on configuration  potentially real-time configuration   For Linux   cat  proc sys fs file-max   will show the current maximum number of file descriptors total allowed to be opened simultaneously  Check out http   www cs uwaterloo ca  brecht servers openfiles html

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10 000  70 000  is that all     FreeBSD is probably the server you want  Here s a little blog post about tuning it to handle 100 000 connections  its has had some interesting features like zero-copy sockets for some time now  along with kqueue to act as a completion port mechanism   Solaris can handle 100 000 connections back in the last century   They say linux would be better  The best description I ve come across is this presentation paper on writing a scalable webserver  He s not afraid to say it like it is        Same for software  the cretins on the   application layer forced great   innovations on the OS layer  Because   Lotus Notes keeps one TCP connection   per client open  IBM contributed major   optimizations for the    one process    100 000 open connections    case to Linux      And the O 1  scheduler was originally   created to score well on some   irrelevant Java benchmark  The bottom   line is that this bloat bene ts all of   us

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Realistically for an application  more then 4000-5000 open sockets on a single machine becomes impractical  Just checking for activity on all the sockets and managing them starts to become a performance issue - especially in real-time environments

User · Answer

depends on the application  if there is only a few packages from each client  100K is very easy for linux  A engineer of my team had done a test years ago  the result shows   when there is no package from client after connection established  linux epoll can watch 400k fd for readablity at cpu usage level under 50

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I achieved 1600k concurrent idle socket connections  and at the same time 57k req s on a Linux desktop  16G RAM  I7 2600 CPU   It s a single thread http server written in C with epoll  Source code is on github  a blog here   Edit   I did 600k concurrent HTTP connections  client  amp  server  on both the same computer  with JAVA Clojure   detail info post  HN discussion  http   news ycombinator com item id 5127251   The cost of a connection with epoll     application need some RAM per connection TCP buffer  2   4k   10k  or more epoll need some memory for a file descriptor  from epoll 7       Each registered file descriptor costs roughly 90                 bytes on a 32-bit kernel  and roughly 160 bytes on a 64-bit kernel

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A limit on the number of open sockets is configurable in the  proc file system  cat  proc sys fs file-max   Max for incoming connections in the OS defined by integer limits   Linux itself allows billions of open sockets   To use the sockets you need an application listening  e g  a web server  and that will use a certain amount of RAM per socket   RAM and CPU will introduce the real limits   modern 2017  think millions not billions   1 millions is possible  not easy  Expect to use X Gigabytes of RAM to manage 1 million sockets   Outgoing TCP connections are limited by port numbers  65000 per IP  You can have multiple IP addresses  but not unlimited IP addresses  This is a limit in TCP not Linux

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Which operating system   For windows machines  if you re writing a server to scale well  and therefore using I O Completion Ports and async I O  then the main limitation is the amount of non-paged pool that you re using for each active connection  This translates directly into a limit based on the amount of memory that your machine has installed  non-paged pool is a finite  fixed size amount that is based on the total memory installed    For connections that don t see much traffic you can reduce make them more efficient by posting  zero byte reads  which don t use non-paged pool and don t affect the locked pages limit  another potentially limited resource that may prevent you having lots of socket connections open     Apart from that  well  you will need to profile but I ve managed to get more than 70 000 concurrent connections on a modestly specified  760MB memory  server  see here  http   www lenholgate com blog 2005 11 windows-tcpip-server-performance html for more details   Obviously if you re using a less efficient architecture such as  thread per connection  or   select  then you should expect to achieve less impressive figures  but  IMHO  there s simply no reason to select such architectures for windows socket servers   Edit  see here http   blogs technet com markrussinovich archive 2009 03 26 3211216 aspx  the way that the amount of non-paged pool is calculated has changed in Vista and Server 2008 and there s now much more available

[linux] How many socket connections possible?

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