On Mon, 18 Apr 2005, Bruce Momjian wrote:
Jeff Davis wrote:
I could still use a little clarification. It seems sort of like there is an extra step, like:
(1) start archiving (2) pg_start_backup() (3) copy PGDATA directory with tar (4) pg_stop_backup() (5) ??
And the text you have at http://candle.pha.pa.us/main/writings/pgsql/sgml/backup-online.html
says: "To make use of this backup, you will need to keep around all the WAL segment files generated during and after the file system backup.".
How long after? Wouldn't you be keeping the WAL segments afterward anyway by archiving?
I've tested and been able to recover using PITR before, but I'd like a little clarification on the steps to make absolutely sure that the base backup I have is viable.
Can you sort of run through the failure case again, and how to prevent it?
The failure case in the original docs is that you do your pg_stop_backup(), and then delete all the WAL file before the *.backup file that was just created. However, you do not have a valid tar backup until you have archived all the WAL files used from the *.backup WAL file up to the WAL file that was active at pg_stop_backup(), which is mentioned in the *.backup file. If you went and deleted your old WAL files anyway, without waiting for those other WAL files to be archived, and your disk drive crashed, you wouldn't have a tar backup you could use, and you had deleted the old WAL files you would have needed to recover your previous tar backup.
Is there something in the current wording that needs clarification?
I'd say it's very not cool :) It's not we all expected from PITR. I recall now Simon mentioned about that and have it in his TODO. Other thing I don't understand what's the problem to generate WAL file by demand ? Probably, TODO should says about this.
Regards, Oleg _____________________________________________________________ Oleg Bartunov, sci.researcher, hostmaster of AstroNet, Sternberg Astronomical Institute, Moscow University (Russia) Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/ phone: +007(095)939-16-83, +007(095)939-23-83
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