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Re: TCP hangs up [message #38631 is a reply to message #38630] Sat, 09 January 2010 09:10 Go to previous messageGo to previous message
nuno is currently offline  nuno
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Registered: January 2010
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Sékiltoyai wrote on Sat, 09 January 2010 01:27
Hello,

Thanks for your answer.

Seems to be ok with your recommend. I have put tcpsndbuf to 48MB:64MB and i can send a 8GB file on my fastest connexion.

Here is the result in ubc :
240: 
kmemsize   2358102  3607954  20971520  31457280  0
...
tcpsndbuf  106952   9038280  50331648  67108864  0
...

So i think a barrier around 10MB will be suitable.



Don't forget that you can have 100 of those connections. Testing is your best bet.

Sékiltoyai wrote on Sat, 09 January 2010 01:27

But i have two questions :
- Is it a normal behaviour that programs (or kernel network driver, i don't know where is the problem) hangs up in case of this tcp buffer shortage ? Isn't there a bug in the kernel, which should simply reject new send() system calls when its buffers are full ?
- Why a call to vzsplit (with a division in 6 vps) gives me a tcpsndbuf of approximately 5.8MB:11MB, so a barrier of 5.8MB, which is far below the needed barrier ?



After faling to allocate memory the TCP connection may be FUBAR (damaged beyond repair).

I never rely on vzsplit. Maybe those numbers will be fine for a 1mbit link? Or for a VPS provider that wants to put 200 containers in a small server? It's a good question for the maintainers.

Regards,

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