PostgreSQL啟動恢復過程中日誌源的切換
阿新 • • 發佈：2018-11-08
日誌源會在XLOG_FROM_ARCHIVE->XLOG_FROM_STREAM->XLOG_FROM_ARCHIVE直接切換，只有讀取過程中出錯，就會切換到另外一個日誌源。但實際執行過程中，XLOG_FROM_ARCHIVE出錯後會到XLOG_FROM_PG_WAL讀取，但是日誌源的變數並不會改變。這個需要注意。
static int
XLogFileReadAnyTLI(XLogSegNo segno, int emode, int source)
{
if (expectedTLEs)
tles = expectedTLEs;
else
tles = readTimeLineHistory(recoveryTargetTLI);
/*
1、WaitForWALToBecomeAvailable呼叫時，source是XLOG_FROM_ARCHIVE時，會使用XLOG_FROM_ANY
2、使用XLOG_FROM_ANY，會首先從歸檔中讀取xlog，如果open失敗，則會使用XLOG_FROM_PG_WAL
3、外部日誌源變數並沒有切換
*/
foreach(cell, tles){
TimeLineID tli = ((TimeLineHistoryEntry *) lfirst(cell))->tli;
if (tli < curFileTLI)
break; /* don't bother looking at too-old TLIs */
if (source == XLOG_FROM_ANY || source == XLOG_FROM_ARCHIVE){
fd = XLogFileRead(segno, emode, tli,XLOG_FROM_ARCHIVE, true);
if (fd != -1){
if (!expectedTLEs)
expectedTLEs = tles;
return fd;
}
}
if (source == XLOG_FROM_ANY || source == XLOG_FROM_PG_WAL){
fd = XLogFileRead(segno, emode, tli, XLOG_FROM_PG_WAL, true);
if (fd != -1){
if (!expectedTLEs)
expectedTLEs = tles;
return fd;
}
}
}
return -1;
}