初步学习pg_control文件之七

接前文 初步学习pg_control文件之六  看   pg_control_version

以PostgreSQL9.1.1为了，其HISTORY文件中有如下的内容：

Release 9.1.2

Release Date: 2011-12-05

This release contains a variety of fixes from 9.1.1. For information
about new features in the 9.1 major release, see the Section called
Release 9.1.

 早就写死了: 

static void
WriteControlFile(void)
{
    ...
    /*
     * Initialize version and compatibility-check fields
     */
    ControlFile->pg_control_version = PG_CONTROL_VERSION;
    ...

}

pg_control.h中有：

/* Version identifier for this pg_control format */
#define PG_CONTROL_VERSION    903

WriteControlFile被  BootStrapXLOG 所调用(仅仅是安装的时候调用一次)