php-fpm配置不当，导致服务器经常出现502错误，上个学期多次调整都没有解决，网上找来资料，大都是增加max_children，可是我都加到顶了，php-fpm log里面还是有大量的警告:
eems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 16 children, there are 0 idle, and 88 total children
不想看英文,一看就头晕,但是502更头晕,特别是昨天,刚重启了lnmp没多久，容不得松口气，就看到负载飙到20多，一开网站，又特么502了。
硬着头皮看默认配置里面的英文注释，才发现自己的三个参数配置貌似有相当大的问题：
Choose how the process manager will control the number of child processes.
; Possible Values:
; static - a fixed number (pm.max_children) of child processes;
; dynamic - the number of child processes are set dynamically based on the
; following directives. With this process management, there will be
; always at least 1 children.
; pm.max_children - the maximum number of children that can
; be alive at the same time.
; pm.start_servers - the number of children created on startup.
; pm.min_spare_servers - the minimum number of children in 'idle'
; state (waiting to process). If the number
; of 'idle' processes is less than this
; number then some children will be created.
; pm.max_spare_servers - the maximum number of children in 'idle'
; state (waiting to process). If the number
; of 'idle' processes is greater than this
; number then some children will be killed.
; ondemand - no children are created at startup. Children will be forked when
; new requests will connect. The following parameter are used:
; pm.max_children - the maximum number of children that
; can be alive at the same time.
; pm.process_idle_timeout - The number of seconds after which
; an idle process will be killed.
; Note: This value is mandatory.
; The number of child processes to be created when pm is set to 'static' and the
; maximum number of child processes when pm is set to 'dynamic' or 'ondemand'.
; This value sets the limit on the number of simultaneous requests that will be
; served. Equivalent to the ApacheMaxClients directive with mpm_prefork.
; Equivalent to the PHP_FCGI_CHILDREN environment variable in the original PHP
; CGI. The below defaults are based on a server without much resources. Don't
; forget to tweak pm.* to fit your needs.
; Note: Used when pm is set to 'static', 'dynamic' or 'ondemand'
; Note: This value is mandatory.
pm.max_children = 5
; The number of child processes created on startup.
; Note: Used only when pm is set to 'dynamic'
; Default Value: min_spare_servers + (max_spare_servers - min_spare_servers) / 2
pm.start_servers = 2
; The desired minimum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.min_spare_servers = 1
; The desired maximum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.max_spare_servers = 3
注释上貌似是说,static模式时,只有pm.max_children生效，dynamic模式时,pm.max_children依然生效，另外:
pm.start_server #控制服务启动时创建的进程数,
pm.min_spare_servers #控制最小备用进程数
pm.max_spare_servers #最大备用进程数
spare_servers翻译成备用进程，不知道合适不适合，如果真这样，那我之前的配置就让人无奈了: pm.min_space_servers 20,pm.max_spare_servers 80，pm.max_children 80，会不会是因为备用的太多才导致502呢？
另外，下面的具体配置里面，注释中给出了计算pm.start_servers默认值的公式：
Default Value: min_spare_servers + (max_spare_servers - min_spare_servers) / 2
按这个公式,我之前的pm.start_servers应该是 20+(80-20)/2=50，可是我当时设置的是20…
重新规划如下:
pm = dynamic
pm.max_children =80
pm.start_servers = 12
pm.min_spare_servers = 4
pm.max_spare_servers = 20
rlimit_files = 65535
pm.max_requests = 102400
貌似要好点了,内存使用不像之前那么夸张了:
