Re: Reading backup label file for checkpoint and redo location during crash recovery

On Mon, Sep 25, 2017 at 7:43 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:

> Greetings Satya,
>
> * Satyanarayana Narlapuram (Satyanarayana(dot)Narlapuram(at)microsoft(dot)com) wrote:
> > During crash recovery, last checkpoint record information is obtained
> from the backup label if present, instead of getting it from the control
> file. This behavior is causing PostgreSQL database cluster not to come up
> until the backup label file is deleted (as the error message says).
> >
> > if (checkPoint.redo < checkPointLoc)
> > {
> > if (!ReadRecord(xlogreader,
> checkPoint.redo, LOG, false))
> > ereport(FATAL,
> > (errmsg("could not
> find redo location referenced by checkpoint record"),
> > errhint("If you are
> not restoring from a backup, try removing the file \"%s/backup_label\".",
> DataDir)));
> > }
> >
> > If we are recovering from a dump file, reading from the backup label
> files makes sense as the control file could be archived after a few
> checkpoints. But this is not the case for crash recovery, and is always
> safe to read the checkpoint record information from the control file.
> > Is this behavior kept this way as there is no clear way to distinguish
> between the recovery from the dump and the regular crash recovery?
>
> This is why the exclusive backup method has been deprecated in PG10 in
> favor of the non-exclusive backup method, which avoids this by not
> creating a backup label file (it's up to the backup software to store
> the necessary information and create the file for use during recovery).
>

Actally, it was deprecated already in 9.6, not just 10.

--
Magnus Hagander
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