How to start slave after pg_basebackup. Why min_wal_size and wal_keep_segments are duplicated

From: "Andrus" <kobruleht2(at)hot(dot)ee>
To: "pgsql-general" <pgsql-general(at)postgresql(dot)org>
Subject: How to start slave after pg_basebackup. Why min_wal_size and wal_keep_segments are duplicated
Date: 2020-05-31 19:47:44
Message-ID: 26EC9619620649D1B55C9C95811E4ADB@dell2
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Hi!

pg_basebackup takes 8 hours.
After it is finished, replication slave does not start:

LOG: consistent recovery state reached at 2DE/985A5BE0
LOG: database system is ready to accept read only connections
LOG: started streaming WAL from primary at 2DE/99000000 on timeline 1
replikaator(at)[unknown] LOG: received replication command: SHOW data_directory_mode
replikaator(at)[unknown] LOG: received replication command: IDENTIFY_SYSTEM
replikaator(at)[unknown] LOG: received replication command: START_REPLICATION 2CF/E9000000 TIMELIN
replikaator(at)[unknown] ERROR: requested WAL segment 00000001000002CF000000E9 has already been re
replikaator(at)[unknown] LOG: received replication command: SHOW data_directory_mode
replikaator(at)[unknown] LOG: received replication command: IDENTIFY_SYSTEM
replikaator(at)[unknown] LOG: received replication command: START_REPLICATION 2CF/E9000000 TIMELIN
replikaator(at)[unknown] ERROR: requested WAL segment 00000001000002CF000000E9 has already been removed
...

i tried it again and same error occured.

How to force replication to start?

I increased wal parameters in master to

wal_compression=on
max_wal_size = 5GB
min_wal_size = 4GB # was 80MB
wal_keep_segments= 360 # was 180

Will this allow replication to start after pg_basebackup ?

According to doc min_wal_size and wal_keep_segments both keep the minimum number of wal segments for replication.
Why those parameters are duplicated?

Andrus.

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