Re: pg_combinebackup does not detect missing files

On 5/17/24 22:20, Robert Haas wrote:
> On Fri, May 17, 2024 at 1:18 AM David Steele <david(at)pgmasters(dot)net> wrote:
>> However, I think allowing the user to optionally validate the input
>> would be a good feature. Running pg_verifybackup as a separate step is
>> going to be a more expensive then verifying/copying at the same time.
>> Even with storage tricks to copy ranges of data, pg_combinebackup is
>> going to aware of files that do not need to be verified for the current
>> operation, e.g. old copies of free space maps.
>
> In cases where pg_combinebackup reuses a checksums from the input
> manifest rather than recomputing it, this could accomplish something.
> However, for any file that's actually reconstructed, pg_combinebackup
> computes the checksum as it's writing the output file. I don't see how
> it's sensible to then turn around and verify that the checksum that we
> just computed is the same one that we now get.

Here's an example. First make a few backups:

$ pg_basebackup -c fast -X none -D test/backup/full -F plain
$ pg_basebackup -c fast -D test/backup/incr1 -F plain -i
/home/dev/test/backup/full/backup_manifest

Then intentionally corrupt a file in the incr backup:

$ truncate -s 0 test/backup/incr1/base/5/3764_fsm

In this case pg_verifybackup will error:

$ pg_verifybackup test/backup/incr1
pg_verifybackup: error: "base/5/3764_fsm" has size 0 on disk but size
24576 in the manifest

But pg_combinebackup does not complain:

$ pg_combinebackup test/backup/full test/backup/incr1 -o test/backup/combine
$ ls -lah test/backup/combine/base/5/3764_fsm
-rw------- 1 dev dialout 0 May 17 22:08 test/backup/combine/base/5/3764_fsm

It would be nice if pg_combinebackup would (at least optionally but
prefferrably by default) complain in this case rather than the user
needing to separately run pg_verifybackup.

Regards,
-David