Re: pg_basebackup problem...

OK, the plot thickens. I've been examining the source code to pg_basebackup
written by Magnus Hagander. It definitely shows that if you do not issue a
"-X f" or "-X s" then the pg_xlogs will NOT be included in the backup. This
leads me to a couple more questions:

1) Does anyone know why anything in a WAL segment is required for a
database to start? I ask this as the backup_label generated by
pg_basebackup indicates a segment where the latest checkpoint is contained.
Surely, there has to be some better way to permit the DB to sanely
initialize. (Note, I haven't yet examined the sources as to how postgres
starts.)

2) If a WAL segment is in fact required for the backed up DB to start, why
would pg_basebackup not include those by default? To not do so, doesn't
create a backup file, just in this case, a tarball that's worthless. After
all, an non-restorable backup, isn't a backup at all.

On Wed, Aug 5, 2015 at 5:00 PM, John Scalia <jayknowsunix(at)gmail(dot)com> wrote:

> Hi all,
>
> We've had a problem surface with the current pg_basebackup procedure we
> were following. Now, I want to explain that this pre-dates me and I
> recommended some additional flags to use when running it, specifically I
> told the group to include "-X f -c fast". Here is the old version they were
> invoking:
>
> pg_basebackup -P -Ft -Z9 -D
> /var/lib/pgsql/9.2/backups/<date_stamped_backup_filename>
>
> The problem we're having, is the tarball these generated will not
> successfully restore. That is, the tarball looks OK, but the resultant
> database cannot be started as the pg_xlog directory is empty and postgres
> says it can't locate the checkpoint segment to sanely initialize.
>
> This really doesn't make sense to me. Shouldn't pg_basebackup capture the
> contents of the pg_xlog directory without needing to use a "-X f" flag?
> Otherwise, why could pg_basebackup create a "backup" that really is not
> usable? I'm really just trying to determine why pg_xlog is empty , if it
> really shouldn't be.
> --
> Jay
>