PostgreSQL启动恢复期间，恢复到的时间线的确定

1、启动恢复时，确定恢复到的时间线recoveryTargetTLI

1）归档恢复点比checkpoint中记录的时间线大，那么选择归档恢复点作为目标时间线

2）否则，checkpoint记录中的时间线作为目标时间线

StartupXLOG->        if (ControlFile->minRecoveryPointTLI >                ControlFile->checkPointCopy.ThisTimeLineID)                recoveryTargetTLI = ControlFile->minRecoveryPointTLI;        else                recoveryTargetTLI = ControlFile->checkPointCopy.ThisTimeLineID;        ...

2、接着从recovery.conf文件中读取

1）若设置了recovery_target_timeline值，并且设为latest，那么history列表最大的时间线即为目标时间线

2）否则是recovery.conf文件中设置的时间线值

3）若没有设置recovery_target_timeline值，则目标时间线为第一步中的值

StartupXLOG->readRecoveryCommandFile()->        for (item = head; item; item = item->next){                if (strcmp(item->name, "restore_command") == 0){                        ...                }else if ...                else if(strcmp(item->name, "recovery_target_timeline") == 0){                        rtliGiven = true;                        if (strcmp(item->value, "latest") == 0)                                rtli = 0;                        else                                rtli = (TimeLineID) strtoul(item->value, NULL, 0);                }else if...        }        if (rtliGiven){                if (rtli){                        recoveryTargetTLI = rtli;                        recoveryTargetIsLatest = false;                }else{                        /* We start the "latest" search from pg_control's timeline */                        recoveryTargetTLI = findNewestTimeLine(recoveryTargetTLI);                        recoveryTargetIsLatest = true;                }        }