Re: Incremental backup from a streaming replication standby fails

Laurenz Albe <laurenz.albe@cybertec.at>

From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Robert Haas <robertmhaas@gmail.com>
Cc: David Steele <david@pgmasters.net>, pgsql-hackers@postgresql.org
Date: 2024-07-22T17:05:46Z
Lists: pgsql-hackers
On Mon, 2024-07-22 at 09:37 -0400, Robert Haas wrote:
> How about something like this:
> 
> An incremental backup is only possible if replay would begin from a
> later checkpoint than for the previous backup upon which it depends.
> On the primary, this condition is always satisfied, because each
> backup triggers a new checkpoint. On a standby, replay begins from the
> most recent restartpoint. As a result, an incremental backup may fail
> on a standby if there has been very little activity since the previous
> backup. Attempting to take an incremental backup that is lagging
> behind the primary (or some other standby) using a prior backup taken
> at a later WAL position may fail for the same reason.

Before I write a v2, a small question for clarification:
I believe I remember that during my experiments, I ran CHECKPOINT
on the standby server between the first backup and the incremental
backup, and that was not enough to make it work.  I had to run
a CHECKPOINT on the primary server.

Does CHECKPOINT on the standby not trigger a restartpoint, or do
I simply misremember?

Yours,
Laurenz Albe



Commits

  1. Document restrictions regarding incremental backups and standbys.