[HACKERS] What does it mean by XLOG_BACKUP_RECORD?

Hi,

While reading source codes I found the following comment in xlog.c.

/** Have we passed our safe starting point? Note that minRecoveryPoint is* known to be incorrectly set if
ControlFile->backupEndRequired,until* the XLOG_BACKUP_RECORD arrives to advise us of the correct* minRecoveryPoint. All
weknow prior to that is that we're not* consistent yet.*/
 
if (!reachedConsistency && !ControlFile->backupEndRequired &&   minRecoveryPoint <= lastReplayedEndRecPtr &&
XLogRecPtrIsInvalid(ControlFile->backupStartPoint))

What does XLOG_BACKUP_RECORED means by? I could not find such XLOG info value.
Does it mean XLOG_BACKUP_END?

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center