我遇到了专用的Ubuntu 12.04 LTS（Apache / 2.2.22），带有APC的PHP 5.3的问题。
每隔几个小时我就会看到这样的情况
[Fri Aug 17 15:36:51 2012] [error] server reached MaxClients setting, consider raising the MaxClients setting 这会导致服务器拒绝/拒绝所有连接。
当我去重新启动Apache：
[Fri Aug 17 15:38:14 2012] [warn] child process 8946 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:14 2012] [warn] child process 7496 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:16 2012] [warn] child process 8946 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:16 2012] [warn] child process 7496 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:18 2012] [warn] child process 8946 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:18 2012] [warn] child process 7496 still did not exit, sending a SIGTERM [Fri Aug 17 15:38:20 2012] [error] child process 8946 still did not exit, sending a SIGKILL [Fri Aug 17 15:38:20 2012] [error] child process 7496 still did not exit, sending a SIGKILL [Fri Aug 17 15:38:21 2012] [notice] caught SIGTERM, shutting down [Fri Aug 17 15:38:21 2012] [warn] Init: Session Cache is not configured [hint: SSLSessionCache] [Fri Aug 17 15:38:22 2012] [notice] Apache/2.2.22 (Ubuntu) PHP/5.3.10-1ubuntu3.2 with Suhosin-Patch mod_ssl/2.2.22 OpenSSL/1.0.1 configured -- resuming normal operations
由于这一切开始发生，我提高了Apache的configuration（这是一个6核心的16Gb内存的机器，所以我想我很多）。
<IfModule mpm_prefork_module> StartServers 8 MinSpareServers 5 MaxSpareServers 10 ServerLimit 500 MaxClients 500 MaxRequestsPerChild 1000 </IfModule>
服务器只提供PHP（没有静态文件），页面加载不会超过几秒钟…
我一直在看mod_status（只是激活它），但我没有看到什么奇怪的…
Server uptime: 20 minutes 46 seconds Total accesses: 9206 - Total Traffic: 641 kB CPU Usage: u147.52 s17.21 cu0 cs0 - 13.2% CPU load 7.39 requests/sec - 526 B/second - 71 B/request 2 requests currently being processed, 8 idle workers ___...W__..._W.....__........................................... ................................................................ ................................................................ ................................................................ ................................................................ ................................................................ ................................................................ ....................................................
我甚至尝试用apache ab来运行一些压力testing，看看能否重现它…没有运气。 🙁
编辑：我刚刚做了一个大发现：
DEBUG: WARNING - require(): GC cache entry '/var/www/common/revisions/1061/library/core/bootstrap.php' (dev=64513 ino=1577080) was on gc-list for 3601 seconds /var/www/common/revisions/1061/library/core/cache/disk/dao.php (16)
这个错误是什么导致的问题，我相信这是与APC有关。
看起来问题是APC内存不足或者某些东西（用于存储操作码的文件），导致Apache下载。 当我把内存限制提高到256M（ apc.shm_size=256M ）时，问题就消失了。
将Apache带到反向代理之后（如nginx，…）在从源代码编译apache之前，需要将“hard-code”放入apache的源代码中，将其从256增加到约2048