Streaming replication is failing with "WAL segment has already been moved" - postgresql

Question

I am trying to implement Master/Slave streaming replication on Postgres 11.5. I ran the following steps -
On Master
select pg_start_backup('replication-setup',true);
On Slave
Stopped the postgres 11 database and ran
rsync -aHAXxv --numeric-ids --progress -e "ssh -T -o Compression=no -x" --exclude pg_wal --exclude postgresql.pid --exclude pg_log MASTER:/var/lib/postgresql/11/main/* /var/lib/postgresql/11/main
On Master
select pg_stop_backup();
On Slave
rsync -aHAXxv --numeric-ids --progress -e "ssh -T -o Compression=no -x" MASTER:/var/lib/postgresql/11/main/pg_wal/* /var/lib/postgresql/11/main/pg_wal
I created the recovery.conf file on slave ~/11/main folder
standby_mode = 'on'
primary_conninfo = 'user=postgres host=MASTER port=5432 sslmode=prefer sslcompression=1 krbsrvname=postgres'
primary_slot_name='my_repl_slot'
When I start Postgres on Slave, I get the error on both MASTER and SLAVE logs -
019-11-08 09:03:51.205 CST [27633] LOG: 00000: database system was interrupted; last known up at 2019-11-08 02:53:04 CST
2019-11-08 09:03:51.205 CST [27633] LOCATION: StartupXLOG, xlog.c:6388
2019-11-08 09:03:51.252 CST [27633] LOG: 00000: entering standby mode
2019-11-08 09:03:51.252 CST [27633] LOCATION: StartupXLOG, xlog.c:6443
2019-11-08 09:03:51.384 CST [27634] LOG: 00000: started streaming WAL from primary at 12DB/C000000 on timeline 1
2019-11-08 09:03:51.384 CST [27634] LOCATION: WalReceiverMain, walreceiver.c:383
2019-11-08 09:03:51.384 CST [27634] FATAL: XX000: could not receive data from WAL stream: ERROR: requested WAL segment 00000001000012DB0000000C has already been removed
2019-11-08 09:03:51.384 CST [27634] LOCATION: libpqrcv_receive, libpqwalreceiver.c:772
2019-11-08 09:03:51.408 CST [27635] LOG: 00000: started streaming WAL from primary at 12DB/C000000 on timeline 1
2019-11-08 09:03:51.408 CST [27635] LOCATION: WalReceiverMain, walreceiver.c:383
The problem is the START WAL - 00000001000012DB0000000C is available right until I run the pg_stop_backup() and is getting archived and no longer available, once the pg_stop_backup() is executed. So this is not an issue of the WAL being archived out due to low WAL_KEEP_SEGMENTS.
postgres#SLAVE:~/11/main/pg_wal$ cat 00000001000012DB0000000C.00000718.backup
START WAL LOCATION: 12DB/C000718 (file 00000001000012DB0000000C)
STOP WAL LOCATION: 12DB/F4C30720 (file 00000001000012DB000000F4)
CHECKPOINT LOCATION: 12DB/C000750
BACKUP METHOD: pg_start_backup
BACKUP FROM: master
START TIME: 2019-11-07 15:47:26 CST
LABEL: replication-setup-mdurbha
START TIMELINE: 1
STOP TIME: 2019-11-08 08:48:35 CST
STOP TIMELINE: 1
My MASTER has archive_command set, and I have the missing WALs available. I copied them into a restore directory on the SLAVE and tried the recovery.conf below, but it still fails with the MASTER reporting the same WAL segment has already been moved error.
Any idea how I can address this issue? I have used rsync to setup replication without any issues in the past on Postgres 9.6, but have been experiencing this issue on Postgres 11.
standby_mode = 'on'
primary_conninfo = 'user=postgres host=MASTER port=5432 sslmode=prefer sslcompression=1 krbsrvname=postgres'
restore_command='cp /var/lib/postgresql/restore/%f %p'

Answer 1

Put a restore_command into recovery.conf that can restore archived WAL files and you are fine.