继续对pgpool-II的child.c里面的 do_child函数进行分析&＃xff0c;改动代码如下&＃xff1a;
/*
* child main loop
*/
void do_child(int unix_fd, int inet_fd)
{
……
for (;;)
{
……
/* perform accept() */
frontend &＃61; do_accept(unix_fd, inet_fd, &timeout);
/*added by gaojian begin*/
if (frontend&＃61;&＃61;NULL)
{
pool_log("frontend is NULL");
}else{
pool_log("frontend is not NULL");
pool_log("I am %d", getpid());
}
/*added by gaojian end*/
if (frontend &＃61;&＃61; NULL) /* connection request from frontend timed out */
{
/* check select() timeout */
if (connected && pool_config->child_life_time > 0 &&
timeout.tv_sec &＃61;&＃61; 0 && timeout.tv_usec &＃61;&＃61; 0)
{
pool_debug("child life %d seconds expired",
pool_config->child_life_time);
/*
* Doesn&＃39;t need to call this. child_exit() calls it.
* send_frontend_exits();
*/
child_exit(2);
}
continue;
}
……
}
child_exit(0);
}
重新编译运行后&＃xff0c;开一个客户端&＃xff0c;显示如下&＃xff1a;
LOG: pid 16210: frontend is not NULL.
LOG: pid 16210: I am 16210
再开一个客户端&＃xff0c;显示如下&＃xff1a;
LOG: pid 16212: frontend is not NULL.
LOG: pid 16212: I am 16212
也就是说&＃xff1a;开一个客户端&＃xff0c;就会有一个child被唤醒
(通过do_accept函数&＃xff0c;虽然大家都调用了do_accept函数&＃xff0c;但是哪个被唤醒当有一个算法)
此时&＃xff0c;kill -9 16210。然后在此客户端再执行sql文&＃xff1a;
select * from a5;
显示&＃xff1a;
postgres&＃61;#select * from a5;
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
postgres&＃61;#
这是&＃xff0c;再看pgpool后台&＃xff0c;
LOG: pid 16216: frontend is not NULL.
LOG: pid 16216: I am 16216
这是因为 Attempting reset, 又唤醒了一个 子进程。
由此可以得到两个结论&＃xff1a;
结论一&＃xff1a;虽然所有的child都会调用 do_child&＃xff0c;在 do_child里调用 do_accept&＃xff0c;但是相当于大家都去申请&＃xff0c;轮到谁来响应客户的请求&＃xff0c;倒不一定。
结论二&＃xff1a;如果某个child不幸挂掉了&＃xff0c;为了继续响应同一个客户端&＃xff0c;另一个child会被唤醒。
本文转自健哥的数据花园博客园博客&＃xff0c;原文链接&＃xff1a;http://www.cnblogs.com/gaojian/archive/2012/07/31/2616769.html&＃xff0c;如需转载请自行联系原作者
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