Re: replication commands and log_statements

On Thu, Aug 14, 2014 at 10:40 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Thu, Aug 14, 2014 at 9:26 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
>> * Amit Kapila (amit(dot)kapila16(at)gmail(dot)com) wrote:
>>> On Wed, Aug 13, 2014 at 4:24 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
>>> > Not entirely sure what you're referring to as 'internally generated'
>>> > here..
>>>
>>> Here 'internally generated' means that user doesn't execute those
>>> statements, rather the replication/backup code form these statements
>>> (IDENTIFY_SYSTEM, TIMELINE_HISTORY, BASE_BACKUP, ...)
>>> and send to server to get the appropriate results.
>>
>> You could argue the same about pg_dump.. I'd not thought of it before,
>> but it might be kind of neat to have psql support "connect in
>> replication mode" and then allow the user to run replication commands.
>
> You can do that by specifying "replication=1" as the conninfo when
> exexcuting psql. For example,
>
> $ psql -d "replication=1"
> psql (9.5devel)
> Type "help" for help.
>
> postgres=# IDENTIFY_SYSTEM;
> systemid | timeline | xlogpos | dbname
> ---------------------+----------+-----------+--------
> 6047222920639525794 | 1 | 0/1711678 |
> (1 row)
More details here:
http://www.postgresql.org/docs/9.4/static/protocol-replication.html

Note as well that not all the commands work though:
=# START_REPLICATION PHYSICAL 0/0;
unexpected PQresultStatus: 8
=# START_REPLICATION PHYSICAL 0/0;
PQexec not allowed during COPY BOTH
We may do something to improve about that but I am not sure it is worth it.
Regards,
--
Michael