barman backup <server> --wait not working with Postgres 17

[cameronmurdoch]

Hi

I set up two otherwise identical postgres servers with barman, once running pg16.6 and the other 17.2, using the following config (XX is the postgres major version):

[servername]
description =  "backup via streaming only"
conninfo = <connstring>
streaming_conninfo = <streaming connstring>
backup_method = postgres
streaming_archiver = on
slot_name = barman
create_slot = auto
path_prefix = "/usr/pgsql-XX/bin"

Both postgres servers are idle. If I run barman backup --wait for the postgres 16 server, I get as expected:

[[email protected] ~]$ barman backup dbpg02 --wait
Starting backup using postgres method for server dbpg02 in /dbfiles/backups/barman/dbpg02/base/20241212T122615
Backup start at LSN: 0/60000C8 (000000010000000000000006, 000000C8)
Starting backup copy via pg_basebackup for 20241212T122615
Copy done (time: 1 second)
Finalising the backup.
Backup size: 5.4 MiB
Backup end at LSN: 0/8000000 (000000010000000000000007, 00000000)
Backup completed (start time: 2024-12-12 12:26:15.062829, elapsed time: 1 second)
Waiting for the WAL file 000000010000000000000007 from server 'dbpg02'
Processing xlog segments from streaming for dbpg02
	000000010000000000000006
Processing xlog segments from streaming for dbpg02
	000000010000000000000007
[[email protected] ~]$

The backup started with walfile 000000010000000000000006 and ended with 000000010000000000000007, and barman receives and archives these as expected almost immediately.

If I do this for the pg17 server, I get this:

[[email protected] ~]$ barman backup dbpg01 --wait
Starting backup using postgres method for server dbpg01 in /dbfiles/backups/barman/dbpg01/base/20241212T122822
Backup start at LSN: 0/5000060 (000000010000000000000005, 00000060)
Starting backup copy via pg_basebackup for 20241212T122822
Copy done (time: 1 second)
Finalising the backup.
Backup size: 6.8 MiB
Backup end at LSN: 0/7000000 (000000010000000000000007, 00000000)
Backup completed (start time: 2024-12-12 12:28:22.841537, elapsed time: 1 second)
Waiting for the WAL file 000000010000000000000007 from server 'dbpg01'
Processing xlog segments from streaming for dbpg01
	000000010000000000000005
	000000010000000000000006

This hangs waiting for walfile 000000010000000000000007, and barman.wal_archiver INFO: No xlog segments found from streaming for dbpg01. is logged constantly in the logfile.

If I manually run switch-wal then the backup completes.

I think this problem is caused by a breaking change in pg17 described in the release notes as:

Change file boundary handling of two WAL file name functions (Kyotaro Horiguchi, Andres Freund, Bruce Momjian) §

The functions pg_walfile_name() and pg_walfile_name_offset() used to report the previous LSN segment number when the LSN was on a file segment boundary; it now returns the current LSN segment.

Here is the commit:
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=344afc776

I see that pg_walfile_name_offset() is used here:

barman/barman/postgres.py

Line 738 in ebffcd3

"({pg_walfile_name_offset}(location)).*, "

And that Backup end at LSN: 0/7000000 (000000010000000000000007, 00000000) is at the segment boundary so for pg <= 16 pg_walfile_name_offset() would have given 000000010000000000000006 as the filename, but for pg17 we get 000000010000000000000007

Thanks!
C

[cameronmurdoch]

Hi,

I've opened a draft PR with quick proof of concept fix that makes barman backup --wait work again on pg17 for me:

#1044

This most likely requires more work :-) and I am unsure if it is even the best approach.

I see also that e.g. pg_walfile_name() is used in switch_wal():

barman/barman/postgres.py

Line 1367 in ebffcd3

def switch_wal(self):

and whilst I guess it is much less likely to encounter a segment boundary here, if it is possible then this function will also need fixing.

Thanks!