PostgreSQL restoration throwing error : replication slot does not exist

Question

Environment: Postgresql 13.x (dockerized)

I was trying to test the DR setup for PostgreSQL nodes. pg_basebackup and wal_files archive was taken from the standby mode.

Done restoration on a new node by copying pg_basebackup and configured postgresql.conf to use restore_command pointing to walfiles archive.

#----------------------- RECOVERY CONFIGS -----------------------
restore_command = 'cp /db-restore/mydb/walfiles/%f "%p"'
recovery_target_timeline = 'latest'
recovery_target_action = promote

• recovery seems to be fine. Some random select queries returning correct results.
• But logfile is throwing below error frequently.

2022-04-19 10:19:53 UTC [291] rep_usr@[unknown] ERROR:  replication slot "slot_name" does not exist
2022-04-19 10:19:58 UTC [296] rep_usr@[unknown] ERROR:  replication slot "slot_name" does not exist

• As I have taken backup from standby, is this restoration making new node as a standby and looking for the replication_slot it used in the previous generation?

• How can I make new node as a Master (remove replication_slot info)

• What are the proper steps to recover if the backup was taken from standby.

• I have 1 master and 2 standby nodes. And planning to take a backup from a standby. So is there any specific changes required for archive_mode and archive_command when using this on a standby node? Current commands:

archive_mode = always
archive_level = logical
archive_command = 'test ! -f /db-archives/walfiles/%f && cp %p /db-archives/walfiles/%f'"

Could someone help with this? Any pointers?

I am sure, db-backup will have info about replication_slot and connection_info as the pg_basebackup itself is a clone of entire DB. To revert configs, I am manually removing postgresql.auto.conf in main directory which contains above parameters.

• So how can I remove any other references of replication_slot if there are any in the DB backup?

Answer 1

I removed all configs and started with fresh.

• removed main/postgresql.auto.conf which was present in the backup.
• main/postgresql.auto.conf is present in standby nodes when we take pg_basebackup. contains the configs used for pg_basebackup in standby nodes. (slot_name, and connect_info).

As I was restoring backup from standby to a Master, I don't need that postgresql.auto.conf.

Answer 2

These error messages don't seem to be thrown by recovery, but by some other tool that connects as database user rep_usr.

Create the replication slot if your application needs it!