Nginx 504 Gateway Time-out 求解

用Nginx 代理 tomcat  每次启动tomcat ，访问页面超过10个就会出现504 Gateway Time-out错误，这是什么原因？nginx配置文件如下，  我不是很懂， 也是照着别人的扒的， worker_processes  1;events {
    worker_connections  2048;
} #events
http {
 
    include mime.types;
default_type application/octet-stream; charset  utf-8;
      
    ssi  on;
  ssi_silent_errors  off;
server_names_hash_bucket_size 128;
client_header_buffer_size 32k;
large_client_header_buffers 4 32k;
client_max_body_size 300m;
      
sendfile on;
tcp_nopush     on; keepalive_timeout 60; tcp_nodelay on; client_body_buffer_size  512k;
proxy_connect_timeout    5;
proxy_read_timeout       60;
proxy_send_timeout       5;
proxy_buffer_size        16k;
proxy_buffers            4 64k;
proxy_busy_buffers_size 128k;
proxy_temp_file_write_size 128k; gzip on;
gzip_min_length  1k;
gzip_buffers     4 16k;
gzip_http_version 1.1;
gzip_comp_level 2;
gzip_vary on;    server {
        listen 81;
root d:/paper/;

rewrite ^/$ /index.do?site=$host:$server_port last;
    rewrite ^/index\.htm$ /index.do?site=$host:$server_port last;
    rewrite ^/(.+)/index\.htm$ /list.do?column=$1&pageNo=1&site=$host:$server_port last;
    rewrite ^/(.+)/index_(\d+)\.htm$ /list.do?column=$1&pageNo=$2&site=$host:$server_port last;
    rewrite ^/(.+)/(\d+-\d+-\d+)/(\d+)\.htm$ /show.do?id=$3&date=$2&column=$1&site=$host:$server_port last;
rewrite ^/block_([\w_]+)\.htm$ /block.do?blockCode=$1&site=$host:$server_port last;
rewrite ^/search\.do$ /search.do?site=$host:$server_port last;
rewrite ^/announce(\d+)\.htm$ /showAnnounce.do?id=$1&site=$host:$server_port last;
rewrite ^/ann\_index\_(\d+)\.htm$ /announceList.do?pageNo=$1&site=$host:$server_port last;

rewrite ^/list\.htm$ /ebook/list.do?pageNo=1&site=$host:$server_port last;
rewrite ^/list_([\d\.]+)\.htm$ /ebook/list.do?cat=$1&pageNo=1&site=$host:$server_port last;
rewrite ^/list_([\d\.]+)_(\d+)\.htm$ /ebook/list.do?cat=$1&pageNo=$2&site=$host:$server_port last;
rewrite ^/list_([\d\.]+)_(\w+)_(\d+)\.htm$ /ebook/list.do?cat=$1&pageNo=1&orderBy=$2&order=$3&site=$host:$server_port last;
rewrite ^/list_([\d\.]+)_(\d+)_(\w+)_(\d+)\.htm$ /ebook/list.do?cat=$1&pageNo=$2&orderBy=$3&order=$4&site=$host:$server_port last;
location / {
         root d:/paper/;
         fastcgi_connect_timeout 600; #set timeout
fastcgi_send_timeout 600;
fastcgi_read_timeout 600;
fastcgi_buffer_size 256k;
fastcgi_buffers 16 256k;
if (!-e $request_filename) {
proxy_pass http://localhost:6080;
         }
proxy_set_header Host $host:81;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Via "nginx";
        }

error_log logs/error.log  debug;
    } #server
} #http