开始
先给 shmem.c 中增加代码(用来打印全局变量 ShmemIndex)
void getmemPointer() { fprintf(stderr,"ShmemIndex ShmemIndex is %ld \n", ShmemIndex); return; }
然后，分别在 bgwriter.c 和 walwriter.c 中，增加如下代码：
/* * Main entry point for bgwriter process * * This is invoked from AuxiliaryProcessMain, which has already created the * basic execution environment, but not enabled signals yet. */ void BackgroundWriterMain(void) { //added by gaojian fprintf(stderr,"BackgroundWriterMain........"); getmemPointer(); … }
/* * Main entry point for walwriter process * * This is invoked from AuxiliaryProcessMain, which has already created the * basic execution environment, but not enabled signals yet. */ void WalWriterMain(void) { //added by gaojian fprintf(stderr,"WalWriterMain..........."); getmemPointer(); ...... }
然后，启动运行后，出现：
[postgres@localhost bin]$ ./postgres -D /usr/local/pgsql/data LOG: database system was shut down at 2012-11-06 16:59:15 CST BackgroundWriterMain........ShmemIndex ShmemIndex is 128175904 WalWriterMain...........ShmemIndex ShmemIndex is 128175904 LOG: autovacuum launcher started LOG: database system is ready to accept connections
得出的结论是，所有的后台进程，恐怕其拥有的指向共享内存的指针，其中的地址完全相同。也就是它们都指向一个共同的共享内存。
结束
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/2012/11/06/2757383.html，如需转载请自行联系原作者
