PostgreSQL Administration - [Fwd: Checkpoint Location Format]

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[Fwd: Checkpoint Location Format]

Andy Shellam

2006-11-07, 7:18 pm

Further to the below e-mail, I've come across a slight problem.
The starting checkpoint location in a backup I've just taken is
"0/22A3190" (note: 7 digits after the /, not 6 as I first thought.)
However the .backup file is called <WAL_FILE>.002A3190 (ie. it only
takes the right-most 6 digits).

Can someone confirm this is the correct case?

Thanks,

Andy.

-------- Original Message --------
Subject: Checkpoint Location Format
Date: Tue, 07 Nov 2006 13:12:53 +0000
From: Andy Shellam (Mailing Lists) <andy.shellam-lists@mailnetwork.co.uk>
To: pgsql-admin@postgresql.org

Hi,

I'm writing an automated file-system level backup application for use
with WAL archiving, that will issue the pg_start_backup call, tar and
gzip the cluster data directory, issue the pg_stop_backup call, and
remove all previous un-needed WAL files from the archive.

I need to write a regular expression that will search for the WAL
filename and checkpoint location from the backup_label file, and just
want to clarify that the checkpoint location will always be of the
format: X/XXXXXX - where X is one of 0-9, A-F?

And then the WAL .backup file that is generated in the archive, has a
filename of the form:

<WAL_FILE>.00XXXXXX.backup

where <WAL_FILE> is the name of the "STARTING WAL LOCATION" directive in
the backup_label file, and XXXXXX is the last 6 digits of the checkpoint
(after the / )?

Thanks,

Andy.

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Tom Lane

2006-11-07, 7:18 pm

"Andy Shellam (Mailing Lists)" <andy.shellam-lists@mailnetwork.co.uk> writes:
> Further to the below e-mail, I've come across a slight problem.
> The starting checkpoint location in a backup I've just taken is
> "0/22A3190" (note: 7 digits after the /, not 6 as I first thought.)
> However the .backup file is called <WAL_FILE>.002A3190 (ie. it only
> takes the right-most 6 digits).

Yeah, the second part of the .backup file name is the offset within the
corresponding WAL file, which for the standard file size of 16M can only
range up to 6 hex digits. The higher-order bits of the second word of
the checkpoint location go into the last part of the WAL file name.
That is, checkpoint location xxxxxxxx/yyzzzzzz should be associated
with a backup file named like ttttttttxxxxxxxx0000
00yy.00zzzzzz.backup.
(I think ... haven't had any caffeine yet this morning ...)

regards, tom lane

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