对pgpool-II的child process的理解(二)

继续对pgpool-II的child.c里面的 do_child函数进行分析,改动代码如下:

/*                                        
* child main loop                                        
*/                                        
void do_child(int unix_fd, int inet_fd)                                        
{                                        
    ……                                  
    for (;;)                                    
    {                          
        ……                             
        /* perform accept() */                                
        frontend = do_accept(unix_fd, inet_fd, &timeout);
        /*added by gaojian begin*/     
            if (frontend==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 == NULL) /* connection request from frontend timed out */ 
        {                                
            /* check select() timeout */                            
            if (connected && pool_config->child_life_time > 0 &&  
                timeout.tv_sec == 0 && timeout.tv_usec == 0)
            {                            
                pool_debug("child life %d seconds expired", 
pool_config->child_life_time); /* * Doesn'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,开一个客户端,显示如下:

LOG: pid 16210: frontend is not NULL.
LOG: pid 16210: I am 16210

再开一个客户端,显示如下:

LOG: pid 16212: frontend is not NULL.
LOG: pid 16212: I am 16212

也就是说:开一个客户端,就会有一个child被唤醒
(通过do_accept函数,虽然大家都调用了do_accept函数,但是哪个被唤醒当有一个算法)

此时,kill  -9  16210。然后在此客户端再执行sql文:

select * from a5;

显示:

postgres=#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=#

这是,再看pgpool后台,

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:

结论一:虽然所有的child都会调用 do_child,在 do_child里调用 do_accept,但是相当于大家都去申请,轮到谁来响应客户的请求,倒不一定。

结论二:如果某个child不幸挂掉了,为了继续响应同一个客户端,另一个child会被唤醒。

posted @ 2012-07-31 14:19  健哥的数据花园  阅读(443)  评论(0编辑  收藏  举报