Re: Log a warning in pg_createsubscriber for max_slot_wal_keep_size

Hi Shubham,

In a previous review [1, comment #3] I was complaining about the lack
of output emitted by the pg_log_debug() because I wanted to see some
LOG evidence of the bad value of max_slot_wal_keep_size.

FYI, I think that mystery has finally been solved.

AFAIK 2 separate problems were contributing to the lack of debug output.

1. Unlike the 'command_ok' subroutine, the 'command_checks_all'
subroutine apparently redirects the output before doing the requested
pattern matching on it. So there is no output to be seen.

2. After that, I did not realise the effect of '-verbose' is
cumulative on loglevel. Specifically, to see debug messages it is not
enough to just say '--verbose'. In fact, you need to specify it 2
times: '--verbose', '--verbose'

~

After addressing these (e.g. by executing the same pg_createsubscriber
using 'command_ok' and using a double '--verbose'), the expected LOGS
can be seen.

e.g. in the file tmp_check/log/regress_log_040_pg_createsubscriber
----------
...
pg_createsubscriber: checking settings on publisher
pg_createsubscriber: publisher: wal_level: logical
pg_createsubscriber: publisher: max_replication_slots: 10
pg_createsubscriber: publisher: current replication slots: 2
pg_createsubscriber: publisher: max_wal_senders: 10
pg_createsubscriber: publisher: current wal senders: 1
pg_createsubscriber: publisher: max_prepared_transactions: 0
pg_createsubscriber: publisher: max_slot_wal_keep_size: 10485760
pg_createsubscriber: warning: publisher requires WAL size must not be restricted
pg_createsubscriber: hint: Set the configuration parameter
"max_slot_wal_keep_size" to -1 to ensure that required WAL files are
not prematurely removed.
pg_createsubscriber: stopping the subscriber
...
----------

See the attached diff for the TAP changes I used to expose this
logging. Apply this atop v8.

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[1] https://www.postgresql.org/message-id/CAHut%2BPszk61QM%2BcEvq_1-A2y%2BJrAD0USB%2BNvtcidajYOfHDkyw%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia