Reply-To: jesper.pedersen@redhat.com
Subject: Re: pg_receivewal documentation
To: Michael Paquier <michael@paquier.xyz>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
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 <20190717013835.GA2130@paquier.xyz>
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 <20190719010903.GC1859@paquier.xyz>
From: Jesper Pedersen <jesper.pedersen@redhat.com>
Organization: Red Hat
Message-ID: <ab8f78b5-4b9f-e31d-daee-c398424fae8c@redhat.com>
Date: Fri, 19 Jul 2019 13:01:27 -0400
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Hi,

On 7/18/19 9:09 PM, Michael Paquier wrote:
>> pg_receivewal -D /tmp/wal -S replica1 --synchronous -h localhost -p 5432 -U
>> repluser -W
>> psql -c 'SELECT * FROM pg_stat_replication;' postgres
>> psql -c 'SELECT * FROM pg_replication_slots;' postgres
>> psql -c 'CREATE DATABASE test' postgres
>>
>> In what scenarios do you see 'on' working ?
> 
> Because the code says so, "on" is an alias for "remote_flush" (which
> is not user-visible by the way):
> src/include/access/xact.h:#define SYNCHRONOUS_COMMIT_ON
> SYNCHRONOUS_COMMIT_REMOTE_FLUSH
> 
> And if you do that it works fine (pg_receivewal --synchronous runs in
> the background and I created a dummy table):
> =# SELECT application_name, sync_state, flush_lsn, replay_lsn FROM
> pg_stat_replication;
>   application_name | sync_state | flush_lsn | replay_lsn
> ------------------+------------+-----------+------------
>   pg_receivewal    | sync       | 0/15E1F88 | null
> (1 row)
> =# set synchronous_commit to on ;
> SET
> =# insert into aa values (2);
> INSERT 0 1
> 

I forgot to use pg_receivewal -d with application_name instead of -h -p -U.

Maybe we should have an explicit option for that, but that is a separate 
thread.

Best regards,
  Jesper