Re: Problem with PITR recovery
От | Bruce Momjian |
---|---|
Тема | Re: Problem with PITR recovery |
Дата | |
Msg-id | 200504170306.j3H36Hr01998@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: Problem with PITR recovery (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Problem with PITR recovery
(Ragnar Hafstað <gnari@simnet.is>)
Re: Problem with PITR recovery (Bruce Momjian <pgman@candle.pha.pa.us>) |
Список | pgsql-hackers |
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > The problem is that we don't archive the partially written xlog file, > > and in this case that xlog file contains the information needed to make > > the tar file consistent. > > > Is this a known problem? Do we document this? If so, I can't find it. > > Yes, and yes. You did not follow the procedure: > > http://www.postgresql.org/docs/8.0/static/backup-online.html#BACKUP-PITR-RECOVERY > > In particular, step 2 says: > > : ... you need at the least to copy the contents of the pg_xlog > : subdirectory of the cluster data directory, as it may contain logs which > : were not archived before the system went down. > > Possibly this needs to be highlighted a little better. I figured that part of the goal of PITR was that you could recover from just the tar backup and archived WAL files --- using the pg_xlog contents is nice, but not something we can require. I understood the last missing WAL log would cause missing information, but not that it would make the tar backup unusable. It would be nice if we could force a new WAL file on pg_stop_backup() and archive the WAL file needed to match the tar file. How hard would that be? I see in the docs: To make use of this backup, you will need to keep around all the WAL segment files generated at or after the starting time of the backup. To aid you in doing this, the pg_stop_backup function creates a backup history file that is immediately stored into the WAL archive area. This file is named after the first WAL segment file that you need to have to make use of the backup. For example, if the starting WAL file is 0000000100001234000055CD the backup history file will be named something like 0000000100001234000055CD.007C9330.backup. (The second part of this file name stands for an exact position within the WAL file, and can ordinarily be ignored.) Once you have safely archived the backup dump file, you can delete all archived WAL segments with names numerically preceding this one. I am not clear on what the "backup dump file" is? I assume it means 0000000100001234000055CD. It is called "WAL segment file" above. I will rename that phrase to match the above terminology. Patch attached and applied. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 Index: doc/src/sgml/backup.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/backup.sgml,v retrieving revision 2.60 diff -c -c -r2.60 backup.sgml *** doc/src/sgml/backup.sgml 23 Mar 2005 19:38:53 -0000 2.60 --- doc/src/sgml/backup.sgml 17 Apr 2005 03:04:35 -0000 *************** *** 733,740 **** the backup history file will be named something like <literal>0000000100001234000055CD.007C9330.backup</>. (The second part of this file name stands for an exact position within the WAL file, and can ! ordinarily be ignored.) Once you have safely archived the backup dump ! file, you can delete all archived WAL segments with names numerically preceding this one. The backup history file is just a small text file. It contains the label string you gave to <function>pg_start_backup</>, as well as the starting and ending times of the backup. If you used the --- 733,740 ---- the backup history file will be named something like <literal>0000000100001234000055CD.007C9330.backup</>. (The second part of this file name stands for an exact position within the WAL file, and can ! ordinarily be ignored.) Once you have safely archived this WAL ! segment file, you can delete all archived WAL segments with names numerically preceding this one. The backup history file is just a small text file. It contains the label string you gave to <function>pg_start_backup</>, as well as the starting and ending times of the backup. If you used the
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