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。
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/08/10/2631881.html，如需转载请自行联系原作者
