【0393】Postgres内核 checkpointer process ③ 构建 WAL records 工作缓存区

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’ <repeats 127 times>,
  RedoRecPtr = 22487440,
  forcePag