i'm facing a lot of TCP timed-out on a busy cache server and here below my sysctl.conf configuration as well as an output of "netstat -st"

Kernel 3.2.0-4-amd64 #1 SMP Debian 3.2.57-3 x86_64 GNU/Linux

Any advice or help would be highly appreciated

cat /etc/sysctl.conf

net.ipv4.tcp_tw_reuse = 1 net.ipv4.tcp_tw_recycle = 1 fs.file-max = 65536 net.ipv4.tcp_low_latency = 1 net.core.wmem_max = 8388608 net.core.rmem_max = 8388608 net.ipv4.ip_local_port_range = 1024 65000 fs.aio-max-nr = 131072 net.ipv4.tcp_fin_timeout = 10 net.ipv4.tcp_keepalive_time = 60 net.ipv4.tcp_keepalive_intvl = 10 net.ipv4.tcp_keepalive_probes = 3 kernel.threads-max = 131072 kernel.msgmax = 32768 kernel.msgmni = 64 kernel.msgmnb = 65536 kernel.shmmax = 68719476736 kernel.shmall = 4294967296 net.ipv4.ip_forward = 1 net.ipv4.tcp_timestamps = 0 net.ipv4.conf.all.accept_redirects = 0 net.ipv4.tcp_window_scaling = 1 net.ipv4.tcp_sack = 0 net.ipv4.tcp_syncookies = 1 net.ipv4.ip_dynaddr = 1 vm.swappiness = 0

vm.drop_caches = 3

net.ipv4.tcp_moderate_rcvbuf = 1 net.ipv4.tcp_no_metrics_save = 1 net.ipv4.tcp_ecn = 0 net.ipv4.tcp_max_orphans = 131072 net.ipv4.tcp_orphan_retries = 1 net.ipv4.conf.default.rp_filter = 0 net.ipv4.conf.default.accept_source_route = 0 net.ipv4.tcp_max_syn_backlog = 32768 net.core.netdev_max_backlog = 131072 net.ipv4.tcp_mem = 6085248 16227328 67108864 net.ipv4.tcp_wmem = 4096 131072 33554432 net.ipv4.tcp_rmem = 4096 174760 33554432 net.core.rmem_default = 33554432 net.core.rmem_max = 33554432 net.core.wmem_default = 33554432 net.core.wmem_max = 33554432 net.core.somaxconn = 10000

/# netstat -st IcmpMsg: InType0: 2 InType3: 233754 InType8: 56251 InType11: 23192 OutType0: 56251 OutType3: 437 OutType8: 4 Tcp: 20680741 active connections openings 63642431 passive connection openings 1126690 failed connection attempts 2093143 connection resets received 13059 connections established 2649651696 segments received 2195445642 segments send out 183401499 segments retransmited 38299 bad segments received. 14648899 resets sent UdpLite: TcpExt: 507 SYN cookies sent 178 SYN cookies received 1376771 invalid SYN cookies received 1014577 resets received for embryonic SYN_RECV sockets 4530970 packets pruned from receive queue because of socket buffer overrun 7233 packets pruned from receive queue 688 packets dropped from out-of-order queue because of socket buffer overrun 12445 ICMP packets dropped because they were out-of-window 446 ICMP packets dropped because socket was locked 33812202 TCP sockets finished time wait in fast timer 622 TCP sockets finished time wait in slow timer 573656 packets rejects in established connections because of timestamp 133357718 delayed acks sent 23593 delayed acks further delayed because of locked socket Quick ack mode was activated 21288857 times 839 times the listen queue of a socket overflowed 839 SYNs to LISTEN sockets dropped 41 packets directly queued to recvmsg prequeue. 79166 bytes directly in process context from backlog 24 bytes directly received in process context from prequeue 2713742130 packet headers predicted 84 packets header predicted and directly queued to user 1925423249 acknowledgments not containing data payload received 877898013 predicted acknowledgments 16449673 times recovered from packet loss due to fast retransmit 17687820 times recovered from packet loss by selective acknowledgements 5047 bad SACK blocks received Detected reordering 11 times using FACK Detected reordering 1778091 times using SACK Detected reordering 97955 times using reno fast retransmit Detected reordering 280414 times using time stamp 839369 congestion windows fully recovered without slow start 4173098 congestion windows partially recovered using Hoe heuristic 305254 congestion windows recovered without slow start by DSACK 933682 congestion windows recovered without slow start after partial ack 77828 TCP data loss events TCPLostRetransmit: 5066 2618430 timeouts after reno fast retransmit 2927294 timeouts after SACK recovery 3059394 timeouts in loss state 75953830 fast retransmits 11929429 forward retransmits 51963833 retransmits in slow start 19418337 other TCP timeouts 2330398 classic Reno fast retransmits failed 2177787 SACK retransmits failed 742371590 packets collapsed in receive queue due to low socket buffer 13595689 DSACKs sent for old packets 50523 DSACKs sent for out of order packets 4658236 DSACKs received 175441 DSACKs for out of order packets received 880664 connections reset due to unexpected data 346356 connections reset due to early user close 2364841 connections aborted due to timeout TCPSACKDiscard: 1590 TCPDSACKIgnoredOld: 241849 TCPDSACKIgnoredNoUndo: 1636687 TCPSpuriousRTOs: 766073 TCPSackShifted: 74562088 TCPSackMerged: 169015212 TCPSackShiftFallback: 78391303 TCPBacklogDrop: 29 TCPReqQFullDoCookies: 507 TCPChallengeACK: 424921 TCPSYNChallenge: 170388 IpExt: InBcastPkts: 351510 InOctets: -609466797 OutOctets: -1057794685 InBcastOctets: 75631402