"Zeugswetter Andreas SB SD" <[EMAIL PROTECTED]> writes: >> Do we need a checkpoint after the archiving >> starts but before the backup begins?
> No. Actually yes. You have to start at a checkpoint record when replaying the log, so if no checkpoint occurred between starting to archive WAL and starting the tar backup, you have a useless backup. It would be reasonable to issue a CHECKPOINT just before starting the backup as part of the standard operating procedure for taking PITR dumps. We need not require this, but it would help to avoid this particular sort of mistake; and of course it might save a little bit of replay effort if the backup is ever used. As far as the business about copying pg_control first goes: there is another way to think about it, which is to copy pg_control to another place that will be included in your backup. For example the standard backup procedure could be 1. [somewhat optional] Issue CHECKPOINT and wait till it finishes. 2. cp $PGDATA/global/pg_control $PGDATA/pg_control.dump 3. tar cf /dev/mt $PGDATA 4. do something to record ending WAL position If we standardized on this way, then the tar archive would automatically contain the pre-backup checkpoint position in ./pg_control.dump, and there is no need for any special assumptions about the order in which tar processes things. However, once you decide to do things like that, there is no reason why the copied file has to be an exact image of pg_control. I claim it would be more useful if the copied file were plain text so that you could just "cat" it to find out the starting WAL position; that would let you determine without any special tools what range of WAL archive files you are going to need to bring back from your archives. This is pretty much the same chain of reasoning that Bruce and I went through yesterday to come up with the idea of putting a label file inside the tar backups. We concluded that it'd be worth putting both the backup starting time and the checkpoint WAL position into the label file --- the starting time isn't needed for restore but might be really helpful as documentation, if you needed to verify which dump file was which. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend