对pgpoo-II的pool_process_context的 proc_id 的理解

最新推荐文章于 2025-08-15 10:38:51 发布

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最新推荐文章于 2025-08-15 10:38:51 发布

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文章标签：数据库

本文解析了pgpool进程上下文中的proc_id概念，并详细解释了其初始化过程及my_proc_id的赋值逻辑，揭示了pgpool进程管理的内部机制。

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已开始，我以为：pool_process_context 里面的 proc_id是其进程ID。其实满不是那么回事：

看Source:

/*                                        
 * Child process context:                                        
 * Manages per pgpool child process context                                        
 */                                        
typedef struct {                                        
    /*                                    
     * process start time, info on connection to backend etc. 
     */                                    
    ProcessInfo   *process_info;                        
    int proc_id;  /* Index to process table(ProcessInfo) (!= UNIX's PID) */        
                                        
    /*                                    
     * PostgreSQL server description. Placed on shared memory. 
     * Includes backend up/down info, hostname, data directory etc.
     */                                    
    BackendDesc *backend_desc;         
    int local_session_id;   /* local session id */                        
                                        
} POOL_PROCESS_CONTEXT;

再看 pool_init_process_context

/*                                    
 * Initialize per process context                                    
 */                                    
void pool_init_process_context(void){                                    
    process_context = &process_context_d; 
    if (!process_info){                                
        pool_error("pool_init_process_context: process_info is not set"); 
        child_exit(1);                            
    }                                
    process_context->process_info = process_info;                                
                                    
    if (!pool_config->backend_desc){                                
        pool_error("pool_init_process_context: backend_desc is not set"); 
        child_exit(1);                            
    }                                
    process_context->backend_desc = pool_config->backend_desc; 
    process_context->proc_id = my_proc_id;  
    process_context->local_session_id = 0;     /* initialize local session counter */            
}

proc_id = my_proc_id。

而 my_proc_id 来自于 main.c 中生成子进程一段：

int my_proc_id;                        
/*                        
* fork a child                        
*/                        
pid_t fork_a_child(int unix_fd, int inet_fd, int id){                        
    pid_t pid;        
    pid = fork();      
    if (pid == 0){                    
        /* Before we unconditionally closed pipe_fds[0] and pipe_fds[1] 
         * here, which is apparently wrong since in the start up of                
         * pgpool, pipe(2) is not called yet and it mistakenly closes
         * fd 0. Now we check the fd > 0 before close(), expecting                
         * pipe returns fds greater than 0.  Note that we cannot                
         * unconditionally remove close(2) calls since fork_a_child()   
         * may be called *after* pgpool starting up.                
         */                
        if (pipe_fds[0] > 0){                
            close(pipe_fds[0]);            
            close(pipe_fds[1]);            
        }                
                        
        myargv = save_ps_display_args(myargc, myargv);                
                        
        /* call child main */                
        POOL_SETMASK(&UnBlockSig);                
        reload_config_request = 0;                
        my_proc_id = id;                
        run_as_pcp_child = false;                
        do_child(unix_fd, inet_fd);                
    }else if (pid == -1){                    
        pool_error("fork() failed. reason: %s", strerror(errno));                
        myexit(1);                
    }                    
    return pid;                    
}

具体来说,在 main.c的代码中，有如下一段。

        /* fork the children */                                    
        for (i=0;i<pool_config->num_init_children;i++){    
            process_info[i].pid = fork_a_child(unix_fd, inet_fd, i); 
            process_info[i].start_time = time(NULL);  
        }

所以，如果pgpool.conf中 num_init_children为128(缺省值)，

那么，每个子进程的 my_proc_id 就会分别是：0,1,2...127。

也就是说，每个子进程的 process_context->proc_id 就是0,1,2,...127。