>Mmm. Maybe something's missing. If you took the base-backup using
>pg_basebackup, that means max_wal_senders > 0 on the primary. If you
>lowered wal_level in the backup (or replica) then started it, You
>would get something like this.
>| FATAL: WAL streaming (max_wal_senders > 0) requires wal_level "replica" or "logical".
>If you changed max_wal_senders to zero, you would get the following instead.
>| FATAL: hot standby is not possible because max_wal_senders = 0 is a lower setting than on the primary server (its value was 2)
Then mark hot_standby off and continue try lowered wal_level.
And do recovery from the basebackup, then you will see the FATAL.
>So I couldn't reproduce the situation.
>Anyways.
>> My question is that what's the mean of [set wal_level to "replica" on the primary] in
>> HINT describe, I can't think over a case to solve this FATAL by set wal_level, I can
>> solve it by turn off hot_standby only.
>>
>> Do you think we can do this code change?
>> --- a/src/backend/access/transam/xlog.c
>> +++ b/src/backend/access/transam/xlog.c
>> @@ -6300,7 +6300,7 @@ CheckRequiredParameterValues(void)
>> if (ControlFile->wal_level < WAL_LEVEL_REPLICA)
>> ereport(ERROR,
>> (errmsg("hot standby is not possible because wal_level was not set to \"replica\" or higher on the primary server"),
>> - errhint("Either set wal_level to \"replica\" on the primary, or turn off hot_standby here.")));
>> + errhint("You should turn off hot_standby here.")));
>Since it's obvious that the change in a primary cannot be propagted by
>taking a backup or starting replication, the first sentence reads to
>me as "you should retake a base-backup from a primary where wal_level
>is replica or higher". So *I* don't think it needs a fix.
I think this HINT is want to guide users to finish this recovery, and the first guide is
invalid in my opinion.