A question about possible recovery inconsistency

Hello.
We had PostgreSQL v11 and used PITR with our database.
But PITR behavior was changed in v13

>https://www.postgresql.org/docs/release/13.0/
>Generate an error if recovery does not reach the specified recovery target (Leif Gunnar Erlandsen, Peter Eisentraut)
>Previously, a standby would promote itself upon reaching the end of WAL, even if the target was not reached.

I tried to change our scripts to include the time where base backup is
started (also I tried the time when the base backup was finished).
But all my recoveries failed with: `XX000: recovery ended before
configured recovery target was reached`

So we decided to use `recovery_target_name` instead of
`recovery_target_time`. But this attempt also failed with the error
above.
Backup procedure looks like this:
1. Insert data
2. t3=$(date +"%Y-%m-%d %T")
3. psql -c "select pg_create_restore_point( '$t3' )"
4. wal-g backup-push $PGDATA. This tool lever low level API
https://www.postgresql.org/docs/current/continuous-archiving.html#BACKUP-LOWLEVEL-BASE-BACKUP.

't3' value was used for `recoverty_target_name`.

Issue here is that `t3` name was not included into base backup and
following WAL files. Logs looks like this:

xargs -n1 '-I{}' docker exec test-userdb-restore psql -d userdb -U
user_api -c 'INSERT INTO test (num) VALUES ({});'
INSERT 0 1
docker exec test-userdb-restore psql -c 'select
pg_create_restore_point( '\''2023-10-10 14:48:46'\'' )'
pg_create_restore_point
-------------------------
0/5000640
(1 row)
wal-g wal-push pg_wal/000000010000000000000006.00000028.backup

/dbdata/postgres/pg_wal:
total 65540
-rw------- 1 postgres postgres 16777216 Oct 10 14:48 000000010000000000000005
-rw------- 1 postgres postgres 16777216 Oct 10 14:48 000000010000000000000006
-rw------- 1 postgres postgres 364 Oct 10 14:48
000000010000000000000006.00000028.backup
-rw------- 1 postgres postgres 16777216 Oct 10 14:48 000000010000000000000007
-rw------- 1 postgres postgres 16777216 Oct 10 14:48 000000010000000000000008
drwx------ 5 postgres postgres 160 Oct 10 14:48 archive_status
drwx------ 3 root root 96 Oct 10 14:48 walg_data

/dbdata/postgres/pg_wal/archive_status:
total 0
-rw------- 1 postgres postgres 0 Oct 10 14:48 000000010000000000000005.done
-rw------- 1 root root 0 Oct 10 14:48
000000010000000000000006.00000028.backup.done
-rw------- 1 root root 0 Oct 10 14:48 000000010000000000000006.done

/dbdata/postgres/pg_wal/walg_data:
total 0
drwx------ 2 postgres postgres 64 Oct 10 14:48 walg_archive_status

/dbdata/postgres/pg_wal/walg_data/walg_archive_status:
total 0
+ docker exec test-userdb-restore bash -c 'cat $PGDATA/pg_wal/$(ls -R
$PGDATA/pg_wal | grep backup | head -n 1)'
START WAL LOCATION: 0/6000028 (file 000000010000000000000006)
STOP WAL LOCATION: 0/6000100 (file 000000010000000000000006)
CHECKPOINT LOCATION: 0/6000060
BACKUP METHOD: streamed
BACKUP FROM: primary
START TIME: 2023-10-10 14:48:46 UTC
LABEL: 2023-10-10 14:48:46.482532 +0000 UTC m=+0.058620814
START TIMELINE: 1
STOP TIME: 2023-10-10 14:48:47 UTC
STOP TIMELINE: 1

When server was stopped couple of WAL files are created:

+ cd /dbdata/postgres/pg_wal
+ ls -R
.:
000000010000000000000006.00000028.backup
000000010000000000000007
000000010000000000000008
000000010000000000000009
00000001000000000000000A
archive_status
walg_data

./archive_status:
000000010000000000000006.00000028.backup.done

**Created `recovery.signal` and started server**
+ echo 'recovery_target_name= '\''2023-10-10 14:48:46'\'''
+ echo 'recovery_target_action= '\''promote'\'''
+ touch /dbdata/postgres/recovery.signal

2023-10-10 14:48:51.825 UTC [127] database system was interrupted;
last known up at 2023-10-10 14:48:46 UTC
2023-10-10 14:48:51.985 UTC [127] LOG: starting point-in-time
recovery to "2023-10-10 14:48:46"
2023-10-10 14:48:52.065 UTC [127] LOG: restored log file
"000000010000000000000006" from archive
2023-10-10 14:48:52.082 UTC [127] LOG: redo starts at 0/6000028
2023-10-10 14:48:52.141 UTC [127] LOG: consistent recovery state
reached at 0/6000100
2023-10-10 14:48:52.141 UTC [124] LOG: database system is ready to
accept read-only connections
2023-10-10 14:48:52.188 UTC [127] LOG: redo done at 0/6000100 system
usage: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.10 s
2023-10-10 14:48:52.188 UTC [127] FATAL: recovery ended before
configured recovery target was reached

See full logs in `experiment1.txt` attachment.

Ok. Some name in the past is not included into the base backup which
was done just now.
This is expected, so I created the named restore point after base backup.

Now logs are:
+ docker exec test-userdb-restore psql -c 'select
pg_create_restore_point( '\''2023-10-10 15:07:37'\'' )'
pg_create_restore_point
-------------------------
0/7000090
(1 row)

+ cat 000000010000000000000006.00000028.backup
START WAL LOCATION: 0/6000028 (file 000000010000000000000006)
STOP WAL LOCATION: 0/6000100 (file 000000010000000000000006)
CHECKPOINT LOCATION: 0/6000060
BACKUP METHOD: streamed
BACKUP FROM: primary
START TIME: 2023-10-10 15:07:37 UTC
LABEL: 2023-10-10 15:07:37.844015 +0000 UTC m=+0.057006433
START TIMELINE: 1
STOP TIME: 2023-10-10 15:07:38 UTC
STOP TIMELINE: 1

2023-10-10 15:07:43.451 UTC [128] LOG: starting point-in-time
recovery to "2023-10-10 15:07:37"
2023-10-10 15:07:43.525 UTC [128] LOG: restored log file
"000000010000000000000006" from archive
2023-10-10 15:07:43.540 UTC [128] LOG: redo starts at 0/6000028
2023-10-10 15:07:43.677 UTC [128] LOG: consistent recovery state
reached at 0/6000100
2023-10-10 15:07:43.677 UTC [128] LOG: recovery stopping at restore
point "2023-10-10 15:07:37", time 2023-10-10 15:07:38.846288+00
2023-10-10 15:07:43.677 UTC [128] LOG: redo done at 0/7000028 system
usage: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.13 s
2023-10-10 15:07:43.677 UTC [125] LOG: database system is ready to
accept read-only connections

1. Why here (in experiment2.txt) redo done at 0/7000028 when recovery
target name "2023-10-10 15:07:37" is at 0/7000090?
I suppose 0/7000090 should be included, because
`recovery_target_inclusive=true` by default.

2. Is there any way to include a label into a base backup which I can
use as `recoverty_target_name`?
This is not clear from documentation
https://www.postgresql.org/docs/current/continuous-archiving.html#BACKUP-LOWLEVEL-BASE-BACKUP
Is 'label' the name for `recovery_target_name` /
`pg_create_restore_point` is called by `pg_backup_start`?

3. Is there any way to get the latest time from a base backup which is
reachable and could be used as the value for `recovery_target_time`?
As a workaround for XX000 error I inserted one additional record into
the database, so a new WAL file is generated. Then I can use the t3
value for `recovery_target_time`.
This only works when archive_command/restore_command was configured.
But without them it seems I can not use the `recovery_target_time`
option. Is this true?

Thank you.

--

Eugen Konkov

DevOps Engineer, Planitar Inc.