You may start postmaster with -d2 option. This will trace your SQL requests.
If you redirect output to a flat file, you will get near a redo log file. The
only thing you have to do is to filter this redo log file to keep only
insert, update, delete SQL statements. So combined with backup, you are able
to rebuild your database until the last instant :
first step you restore from last backup
second step apply updates kept in redo log file
The matter is to synchronize "end of backup" and "begin of redo log". You may
stop postmaster, do a cold backup, and then restart postmaster on a new redo
log.
Jerome