John R Pierce wrote: > to copy the data directory and have it be useful you need to bracket the copy with calls to > pg_start_backup() and pg_stop_backup() .... this ensures the data files are coherent. this is in > fact what pg_basebackup does for you....
I apologize for my fussiness, but this is a misconception I encounter so frequently that I have to speak up.
The file system copy does not become consistent (isn't that what you meant?) if it is surrounded by pg_start_backup() and pg_stop_backup(). What happens is that a) a backup.label file is created that tells recovery where to start b) more WAL is generated so that all changes can be replayed safely.