Re: backup manifests

On Thu, Sep 19, 2019 at 9:51 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> I intend that we should be able to support incremental backups based
> either on a previous full backup or based on a previous incremental
> backup. I am not aware of a technical reason why we need to identify
> the specific backup that must be used. If incremental backup B is
> taken based on a pre-existing backup A, then I think that B can be
> restored using either A or *any other backup taken after A and before
> B*. In the normal case, there probably wouldn't be any such backup,
> but AFAICS the start-LSNs are a sufficient cross-check that the chosen
> base backup is legal.

Scratch that: there can be overlapping backups, so you have to
cross-check both start and stop LSNs.

> > > (3) Cross-check a manifest against a backup and complain about extra
> > > files, missing files, size differences, or checksum mismatches.
> >
> > Verification is the best part of the manifest. Plus, you can do
> > verification pretty cheaply on restore. We also restore pg_control last
> > so clusters that have a restore error won't start.
>
> There's no "restore" operation here, really. A backup taken by
> pg_basebackup can be "restored" by copying the whole thing, but it can
> also be used just where it is. If we were going to build something
> into some in-core tool to copy backups around, this would be a smart
> way to implement said tool, but I'm not planning on that myself.

Scratch that: incremental backups need a restore tool, so we can use
this technique there. And it can work for full backups too, because
why not?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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