在创建了太多的vhost之后，Apache停止了与memcache的通信。

Question

我注意到Apache有一个很奇怪的问题。我有一个非常多的虚拟主机设置-它大约是501。

在vhost编号493之后开始出现问题。前493个vhost按预期工作，但当我添加vhost编号494时，PHP就停止与memcache的通信，并在每次读/写访问中超时。

实际上，我使用memcache作为后端会话存储，所以，php函数：

session_start();

30秒后就可以超时了。

如果我删除494个vhost中的随机一个并重新启动apache，它将再次开始工作。

我设定了很高的上限(65k)，但没有帮助。我试过完全关闭上限，但没有运气。

你们知不知道我还能再试试什么？

在浏览器中单击enter之后，在30秒后开始等待，我已经尝试了连接到的httpd进程。

这是strace输出：

select(1170, [1024 1169], [], NULL, {1, 0}) = 2 (in [1024 1169], left {0, 999998})
select(1170, [1024 1169], [], NULL, {1, 0}) = 2 (in [1024 1169], left {0, 999998})
select(1170, [1024 1169], [], NULL, {1, 0}) = 2 (in [1024 1169], left {0, 999998})
select(1170, [1024 1169], [], NULL, {1, 0}) = 2 (in [1024 1169], left {0, 999998})
select(1170, [1024 1169], [], NULL, {1, 0}) = 2 (in [1024 1169], left {0, 999998})

因此，apache基本上停留在select()上，仅此而已，它无限期地重复select()系统调用。

接下来，我想出了tcpdump，看看包是否真的通过apache，而且它确实是这样做的：

22:11:28.366677 IP6 ::1.51404 > ::1.11914: Flags [S], seq 2899674987, win 32752, options [mss 16376,sackOK,TS val 1384759049 ecr 0,nop,wscale 9], length 0
22:11:28.366697 IP6 ::1.11914 > ::1.51404: Flags [S.], seq 2034630080, ack 2899674988, win 32728, options [mss 16376,sackOK,TS val 1384759049 ecr 1384759049,nop,wscale 9], length 0
22:11:28.366709 IP6 ::1.51404 > ::1.11914: Flags [.], ack 1, win 64, options [nop,nop,TS val 1384759049 ecr 1384759049], length 0
22:11:28.366752 IP6 ::1.51404 > ::1.11914: Flags [P.], seq 1:41, ack 1, win 64, options [nop,nop,TS val 1384759049 ecr 1384759049], length 40
22:11:28.366758 IP6 ::1.11914 > ::1.51404: Flags [.], ack 41, win 64, options [nop,nop,TS val 1384759049 ecr 1384759049], length 0
22:11:28.366768 IP6 ::1.51404 > ::1.11914: Flags [P.], seq 41:90, ack 1, win 64, options [nop,nop,TS val 1384759050 ecr 1384759049], length 49
22:11:28.366772 IP6 ::1.11914 > ::1.51404: Flags [.], ack 90, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 0
22:11:28.366779 IP6 ::1.51404 > ::1.11914: Flags [P.], seq 90:122, ack 1, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 32
22:11:28.366783 IP6 ::1.11914 > ::1.51404: Flags [.], ack 122, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 0
22:11:28.367063 IP6 ::1.11914 > ::1.51404: Flags [P.], seq 1:12, ack 122, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 11
22:11:28.367070 IP6 ::1.51404 > ::1.11914: Flags [.], ack 12, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 0
22:11:28.367266 IP6 ::1.11914 > ::1.51404: Flags [P.], seq 12:20, ack 122, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 8
22:11:28.367275 IP6 ::1.51404 > ::1.11914: Flags [.], ack 20, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 0
22:11:28.367477 IP6 ::1.11914 > ::1.51404: Flags [P.], seq 20:25, ack 122, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 5
22:11:28.367489 IP6 ::1.51404 > ::1.11914: Flags [.], ack 25, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 0
22:11:28.367629 IP6 ::1.51404 > ::1.11914: Flags [P.], seq 122:181, ack 25, win 64, options [nop,nop,TS val 1384759050 ecr 1384759050], length 59
22:11:28.367859 IP6 ::1.11914 > ::1.51404: Flags [P.], seq 25:33, ack 181, win 64, options [nop,nop,TS val 1384759051 ecr 1384759050], length 8
22:11:28.367869 IP6 ::1.51404 > ::1.11914: Flags [P.], seq 181:230, ack 33, win 64, options [nop,nop,TS val 1384759051 ecr 1384759051], length 49
22:11:28.368102 IP6 ::1.11914 > ::1.51404: Flags [P.], seq 33:41, ack 230, win 64, options [nop,nop,TS val 1384759051 ecr 1384759051], length 8
22:11:28.368138 IP6 ::1.51404 > ::1.11914: Flags [F.], seq 230, ack 41, win 64, options [nop,nop,TS val 1384759051 ecr 1384759051], length 0
22:11:28.368195 IP6 ::1.11914 > ::1.51404: Flags [F.], seq 41, ack 231, win 64, options [nop,nop,TS val 1384759051 ecr 1384759051], length 0
22:11:28.368206 IP6 ::1.51404 > ::1.11914: Flags [.], ack 42, win 64, options [nop,nop,TS val 1384759051 ecr 1384759051], length 0

接下来我做的是Apache的GDB，当我对包含session_start()的页面发出curl调用时，这是输出：

232     *(*new)->local_addr = *sock->local_addr;
241     if (sock->local_addr->sa.sin.sin_family == AF_INET) {
238     (*new)->local_addr->pool = connection_context;
241     if (sock->local_addr->sa.sin.sin_family == AF_INET) {
238     (*new)->local_addr->pool = connection_context;
241     if (sock->local_addr->sa.sin.sin_family == AF_INET) {
245     else if (sock->local_addr->sa.sin.sin_family == AF_INET6) {
246         (*new)->local_addr->ipaddr_ptr = &(*new)->local_addr->sa.sin6.sin6_addr;
249     (*new)->remote_addr->port = ntohs((*new)->remote_addr->sa.sin.sin_port);
250     if (sock->local_port_unknown) {
256     if (apr_is_option_set(sock, APR_TCP_NODELAY) == 1) {
257         apr_set_option(*new, APR_TCP_NODELAY, 1);
266     if (sock->local_interface_unknown ||
267         !memcmp(sock->local_addr->ipaddr_ptr,
266     if (sock->local_interface_unknown ||
276         (*new)->local_interface_unknown = 1;
293     apr_pool_cleanup_register((*new)->pool, (void *)(*new), socket_cleanup,
292     (*new)->inherit = 0;
293     apr_pool_cleanup_register((*new)->pool, (void *)(*new), socket_cleanup,
296 }   
unixd_accept (accepted=0x7fff14ecddf0, lr=0x7fe93a905aa8, ptrans=<value optimized out>) at /usr/src/debug/httpd-2.2.15/os/unix/unixd.c:507
507     if (status == APR_SUCCESS) {
508         *accepted = csd;
649 }   
child_main (child_num_arg=<value optimized out>) at /usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:650
650         SAFE_ACCEPT(accept_mutex_off());      /* unlock after "accept" */
652         if (status == APR_EGENERAL) {
656         else if (status != APR_SUCCESS) {
665         current_conn = ap_run_create_connection(ptrans, ap_server_conf, csd, my_child_num, sbh, bucket_alloc);
666         if (current_conn) {
667             ap_process_connection(current_conn, csd);

在这个位置有一个很大的暂停(~30秒)，直到php超时。在那之后，我得到了这个：

668             ap_lingering_close(current_conn);
676         if (ap_mpm_pod_check(pod) == APR_SUCCESS) { /* selected as idle? */
680                  ap_scoreboard_image->global->running_generation) { /* restart? */
679         else if (ap_my_generation !=
680                  ap_scoreboard_image->global->running_generation) { /* restart? */
679         else if (ap_my_generation !=
551     while (!die_now && !shutdown_pending) {
559         apr_pool_clear(ptrans);
562              && requests_this_child++ >= ap_max_requests_per_child)) { 
561         if ((ap_max_requests_per_child > 0
562              && requests_this_child++ >= ap_max_requests_per_child)) {
561         if ((ap_max_requests_per_child > 0
562              && requests_this_child++ >= ap_max_requests_per_child)) {
561         if ((ap_max_requests_per_child > 0
566         (void) ap_update_child_status(sbh, SERVER_READY, (request_rec *) NULL);
573         SAFE_ACCEPT(accept_mutex_on());
575         if (num_listensocks == 1) {

最奇怪的是我不能在另一台机器上复制这个。相同的操作系统，相同的软件包，相同的配置(傀儡)相同的内核，不同的HW。

Answer 1

经过几个星期的调试和注意问题，我终于无意中发现了一条消息：

You MUST recompile PHP with a larger value of FD_SETSIZE.
It is set to 1024, but you have descriptors numbered at least as high as 1073.
--enable-fd-setsize=2048 is recommended, but you may want to set it to equal
the maximum number of open files supported by your system, in order to avoid
seeing this error again at a later date. 

我会尝试这个修复，但是孩子们，为什么PHP会这么做呢？这是如此丑陋，硬编码的无文件限制是完全打破设计。更不用说，如果这是解决方案，迫使我重新编译每个PHP小版本和安全修补程序并维护自己的包是一个很大的麻烦。

编辑:经过更广泛的调试后，似乎不仅仅是PHP“被设计破坏了”，而且memcache扩展本身也存在一系列问题。

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=629896

https://bugs.php.net/bug.php?id=59876

Bug现在已经开放了很长一段时间了，什么也没有发生。我想我们应该转储memcache扩展，并找到一个独立于它的解决方案:-/