Question

我有时发现来自客户端超时的请求。我在服务器端使用tcpdump捕获一些特殊的tcp数据包，如下所示。似乎没有数据包丢失。为什么服务器在收到第一个SYN后没有回复客户端？ enter image description here

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
SYN_RECV 220
CLOSE_WAIT 1
ESTABLISHED 496
FIN_WAIT1 42
FIN_WAIT2 2
TIME_WAIT 72588

sysctl -a | grep tcp
net.ipv4.tcp_abort_on_overflow = 0
net.ipv4.tcp_adv_win_scale = 1
net.ipv4.tcp_allowed_congestion_control = cubic reno
net.ipv4.tcp_app_win = 31
net.ipv4.tcp_available_congestion_control = cubic reno
net.ipv4.tcp_base_mss = 512
net.ipv4.tcp_challenge_ack_limit = 100
net.ipv4.tcp_congestion_control = cubic
net.ipv4.tcp_dsack = 1
net.ipv4.tcp_early_retrans = 3
net.ipv4.tcp_ecn = 2
net.ipv4.tcp_fack = 1
net.ipv4.tcp_fastopen = 0
net.ipv4.tcp_fastopen_key = fc1980cc-2a3369bf-91223671-bb8e012f
net.ipv4.tcp_fin_timeout = 60
net.ipv4.tcp_frto = 2
net.ipv4.tcp_init_cwnd = 10
net.ipv4.tcp_keepalive_intvl = 75
net.ipv4.tcp_keepalive_probes = 9
net.ipv4.tcp_keepalive_time = 7200
net.ipv4.tcp_limit_output_bytes = 131072
net.ipv4.tcp_loss_init_cwnd = 1
net.ipv4.tcp_low_latency = 0
net.ipv4.tcp_max_orphans = 524288
net.ipv4.tcp_max_ssthresh = 0
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_max_tw_buckets = 524288
net.ipv4.tcp_mem = 761319   1015094 1522638
net.ipv4.tcp_min_tso_segs = 2
net.ipv4.tcp_moderate_rcvbuf = 1
net.ipv4.tcp_mtu_probing = 0
net.ipv4.tcp_no_delay_ack = 0
net.ipv4.tcp_no_metrics_save = 0
net.ipv4.tcp_orphan_retries = 0
net.ipv4.tcp_reordering = 3
net.ipv4.tcp_retrans_collapse = 1
net.ipv4.tcp_retries1 = 3
net.ipv4.tcp_retries2 = 15
net.ipv4.tcp_rfc1337 = 0
net.ipv4.tcp_rmem = 4096    87380   6291456
net.ipv4.tcp_sack = 1
net.ipv4.tcp_slow_start_after_idle = 1
net.ipv4.tcp_stdurg = 0
net.ipv4.tcp_syn_retries = 6
net.ipv4.tcp_synack_retries = 5
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_thin_dupack = 0
net.ipv4.tcp_thin_linear_timeouts = 0
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tso_win_divisor = 3
net.ipv4.tcp_tw_ignore_syn_tsval_zero = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_recycle_private_only = 0
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_wmem = 4096    16384   4194304
net.ipv4.tcp_workaround_signed_windows = 0

我尝试设置tcp_tw_reuse tcp_tw_recycle并增加tcp_max_syn_backlog。仍然出现错误：error = HTTP 599：连接时超时，headers = tornado.httputil.HTTPHeaders对象为0x7f74ed884860，reason ='Unknown'

Answer 1

服务器的TCP连接积压可能已满。

man page of listen说：

如果基础协议支持重新传输，该请求可能会被忽略，以便稍后重新尝试连接成功。

尝试增加服务器backlog调用的listen()参数值。

服务器立即从客户端收到SYN后发送SYN / ACK

1 个答案: