Re: Re: [COMMITTERS] pgsql: Map basebackup tablespaces using a tablespace_map file

On Tue, Jun 9, 2015 at 9:09 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
> On Tue, May 12, 2015 at 10:42 PM, Andrew Dunstan <andrew(at)dunslane(dot)net>
wrote:
> > Map basebackup tablespaces using a tablespace_map file
> >
> > Windows can't reliably restore symbolic links from a tar format, so
> > instead during backup start we create a tablespace_map file, which is
> > used by the restoring postgres to create the correct links in pg_tblspc.
> > The backup protocol also now has an option to request this file to be
> > included in the backup stream, and this is used by pg_basebackup when
> > operating in tar mode.
> >
> > This is done on all platforms, not just Windows.
> >
> > This means that pg_basebackup will not not work in tar mode against 9.4
> > and older servers, as this protocol option isn't implemented there.
>
> While I was performing the recovery-related tests, I found that there was
> the case where $PGDATA/tablespace_map was not renamed to *.old at the
recovery.
> Is this harmless and intentional?

There shouldn't be any problem because we tablespace_map file
only if backup file is present.

> Sorry if this has been already
> discussed so far.
>
> The steps to reproduce the problem is:
>
> 1. start base backup, i.e., call pg_start_backup().
> 2. repeat some write transactions and checkpoints until the WAL file
containing
> the checkpoint record that backup_label indicates will be removed.
> 3. killall -9 postgres
> 4. start the server and a crash recovery.
>
> At this time, the crash recovery fails with the following error messages.
> 2015-06-09 12:26:54 JST FATAL: could not locate required checkpoint
record
> 2015-06-09 12:26:54 JST HINT: If you are not restoring from a backup,
> try removing the file ".../backup_label".
>
> 5. according to the above hint message, remove $PGDATA/backup_label
> and restart a crash recovery
>
> Then you can see that tablespace_map remains in $PGDATA after the
recovery ends.
>

The basic idea is that tablespace_map file will be used in case we
have to restore from a backup which contains tablespaces. So
I think if user is manually removing backup_label, there is no
meaning of tablespace_map, so that should also be removed. One
way to address this is modify the Hint message suggesting that
remove tablespace_map if present.

Current :
If you are not restoring from a backup, try removing the file
\"%s/backup_label\
Modify it to:
If you are not restoring from a backup, try removing the file
\"%s/backup_label\
and, if present \"%s/tablespace_map\.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com