对PostgreSQL中 共享内存指针的再认识

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