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I have 2 servers set up with about 80ms latency between them. Both are centos 6 and run a java app that transfers data from on location to another. Both are on 1gbps connections.

I have been trying different sysctl settings and different send & receive buffer settings in java but no matter what I set them to, I cannot get the tcp window size to go above 130048 in the tcp dumps. This equates to roughly 13mbps which is the actual throughput I am getting.

Current sysctl settings are:

net.core.wmem_max = 16777216
net.core.rmem_max = 16777216
net.core.wmem_default = 2400000
net.core.rmem_default = 2400000
net.ipv4.tcp_wmem = 4096    65536 16777216
net.ipv4.tcp_rmem = 4096    87380 16777216 
  • Can you show your sysctl.conf settings? – ewwhite Oct 2 '12 at 8:42
  • Sure, net.core.wmem_max = 16777216 net.core.rmem_max = 16777216 net.core.wmem_default = 2400000 net.core.rmem_default = 2400000 net.ipv4.tcp_wmem = 4096 65536 16777216 net.ipv4.tcp_rmem = 4096 87380 16777216 – Roger Oct 2 '12 at 9:08
  • 1Gbps at 80ms gives a Bandwidth Delay Product of just under 10Mb. Try increasing your socket buffers? 4096 10485760 33554432 – suprjami May 18 '13 at 13:42

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