Consistent backup
It is the backup taken when all committed transactions are written to the database
files, i.e., all the dirty buffer in memory is written to disk.
Consistent backup can be taken by stopping the database in smart/fast mode.
Inconsistent/Online Backup
It is the backup taken when the data files are not up-to-date, i.e., all committed
transactions have not been written to the data files. In other words, it is the backup
taken when the dirty buffer in the memory has not been written to the disk yet.
Databases that need to work 24/7, that cannot be stopped, are backed up online
(inconsistent).
Complete Recovery
The database is restored from the backup until the last committed transaction.
First, restore from the backup taken with pg_basebackup, then the wal files are
processed.
Point-In Recovery
By entering the time in the recover_target_time parameter, it is possible to
restore to a point between the full backup and the last wal file.
For example, a full backup was taken at 03:00 at night.
There are wal files until 17:00 in the evening.
It can be recovered to 13:05 with recover_target_time = “YYYY-MM-DD 13:05".