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< Advanced Erlang/OTP ~ gen_tcp and the undocumented buffer option |
| rikshot |
 Posted: Tue Mar 24, 2009 2:05 am |
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Joined: 24 Mar 2009
Posts: 1
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| I'm trying to control the amount of data that gen_tcp sends when the socket is set to active mode. It seems that the undocumented 'buffer' option controls the limit when gen_tcp send a message. The default value is 1460. When I set the buffer option to something smaller than the default value, it does whats expected, and limits the message size to for example 1024. However, when I change the value something larger than the default, for example 2048, it still limits the messages sent to the default 1460 value. What's going on? Is this a bug or should I be setting something else also? |
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| uwiger |
| Posted: Tue Mar 24, 2009 4:36 pm |
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Joined: 03 Jul 2006
Posts: 604
Location: Sweden
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rikshot wrote: I'm trying to control the amount of data that gen_tcp sends when the socket is set to active mode. It seems that the undocumented 'buffer' option controls the limit when gen_tcp send a message.
Answer relayed from Erlang/OTP guru Raimo Niskanen:
Try and play with the options 'sndbuf', 'recbuf', and 'buffer'. Use inet:getopts to see what they are per default.
'buffer' is the size of the buffer used by the inet driver when receiving data from the kernel.
'sndbuf' and 'recbuf' corresponds to the socket options SO_SNDBUF and SO_RCVBUF. See the man pages; they say (socket(7) on SLES 10) something about returning the double size with getsockopt... Strange.
Furhermore, the inet driver adjusts the 'buffer' value so it is no less than the 'sndbuf' and 'recbuf' values when you change them, making things even more interesting.
You can also count on TCP destroying any assumtion you can have on the size of the received blocks. All you can depend on is that the bytes comes in the order as sent. |
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| rbucker881 |
| Posted: Wed Apr 01, 2009 8:48 pm |
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Joined: 11 Oct 2007
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I have not looked at this issue.... however, 1460 rings a bell. I think it's one of those magic numbers that might sync with the MTU.
/r |
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| wuji |
| Posted: Mon Aug 13, 2012 7:04 am |
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| wantjersey |
| Posted: Fri Aug 17, 2012 6:06 am |
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