1. 初始化 ThisTimeLineID、RedoRecPtr
函数 InitXLOGAccess() 内部会初始化 ThisTimeLineID、wal_segment_size、doPageWrites 和 RedoRecPtr 等全局变量。
下面是这四个变量初始化前的值：
- (gdb) p ThisTimeLineID
$125 =0
(gdb) p wal_segment_size
$126 =16777216
(gdb) p doPageWrites
$127 =false
(gdb) p RedoRecPtr
$128 =0
XlogCtl 变量成员初始化情况如下：
- (gdb) p
*XLogCtl
$130 = {
Insert = {
insertpos_lck = 0 ‘\000’,
CurrBytePos = 22421680,
PrevBytePos = 22421624,
pad = ‘\000’ <repeat
