On 9/19/19 11:00 AM, Robert Haas wrote:
On Thu, Sep 19, 2019 at 9:51 AM Robert Haas <robertmh...@gmail.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.
Overall we have found it's much simpler to label each backup and
cross-check that against the pg version and system id. Start LSN is
pretty unique, but backup labels work really well and are more widely
understood.
(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?
Agreed, once we have a restore tool, use it for everything.
--
-David
da...@pgmasters.net
