189 8069 5689
PostgreSQL在shutdown时会进行checkpoint。其流程如下。
成都创新互联是一家集网站建设,察隅企业网站建设,察隅品牌网站建设,网站定制,察隅网站建设报价,网络营销,网络优化,察隅网站推广为一体的创新建站企业，帮助传统企业提升企业形象加强企业竞争力。可充分满足这一群体相比中小企业更为丰富、高端、多元的互联网需求。同时我们时刻保持专业、时尚、前沿，时刻以成就客户成长自我，坚持不断学习、思考、沉淀、净化自己，让我们为更多的企业打造出实用型网站。
1、在主进程中，会首先注册一个信号处理函数reaper，用于向checkpoint等子进程发送信号。向checkpoint进程发送SIGUSR2信号
PostmasterMain(int argc, char argv[])
pqsignal_no_restart(SIGCHLD, reaper); / handle child termination */
reaper：
while ((pid = waitpid(-1, &exitstatus, WNOHANG)) > 0){
...
if (pid == CheckpointerPID){
...
SignalChildren(SIGUSR2);
}
...
}
...
PostmasterStateMachine();//向checkpoint进程发送SIGUSR2信号
|-----------------------
| if (pmState == PM_WAIT_BACKENDS){
| if (CountChildren(BACKEND_TYPE_NORMAL | BACKEND_TYPE_WORKER) == 0 &&
| StartupPID == 0 &&
| WalReceiverPID == 0 &&
| BgWriterPID == 0 &&
| (CheckpointerPID == 0 ||(!FatalError && Shutdown < ImmediateShutdown)) &&
| WalWriterPID == 0 &&
| AutoVacPID == 0){
| //pg_ctl stop -m immediate不会向checkpoint进程发送信号，即不会做checkpoint
| if (Shutdown >= ImmediateShutdown || FatalError){
| pmState = PM_WAIT_DEAD_END;
| }else{
| if (CheckpointerPID != 0){
| signal_child(CheckpointerPID, SIGUSR2);
| pmState = PM_SHUTDOWN;
| }
}
| }
|-------}
2、checkpoint进程，也会注册一个信号处理函数ReqShutdownHandler，用于处理主进程发送过来的SIGUSR2信号。接收到该信号后将shutdown_requested置为TRUE。在checkpoint进程的for循环中，如果shutdown_requested为TRUE，则进入shutdown流程：stop每个sender进程，所有sender进程stop后，根据条件进行checkpoint：CreateRestartPoint后者CreateCheckPoint
CheckpointerMain(void)->
//为信号SIGUSR2安装信号处理函数ReqShutdownHandler
pqsignal(SIGUSR2, ReqShutdownHandler); / request shutdown /
...
for (;;){
if (shutdown_requested){
/ Close down the database /
ShutdownXLOG(0, 0);
|-- WalSndInitStopping();//向每个sender进程发送信号修改到stopping状态
| WalSndWaitStopping();
| if (RecoveryInProgress())
| CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
| else{
| if (XLogArchivingActive() && XLogArchiveCommandSet())
| RequestXLogSwitch(false);
| CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
| }
|-- ...
proc_exit(0);
}
...
checkpoint
}
3、ReqShutdownHandler函数将shutdown_requested置为TRUE
ReqShutdownHandler(SIGNAL_ARGS)
{
shutdown_requested = true;
SetLatch(MyLatch);
}