Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.

On Thursday, March 23, 2017 4:50:20 AM EDT Magnus Hagander wrote:
> We should probably consider if there is some way we can implement
> these two things the same way. If we're inventing a new variable that
> gets pushed on each connection, perhaps we can use that one and avoid
> the SHOW command? Is the read-write thing really interesting in the
> aspect of the general case, or is it more about detectinv readonly
> standbys as well? Or to flip that, would sending the
> transaction_read_only parameter be enough for the usecase in this
> thread, without having to invent a new variable?

Hot standby differs from regular read-only transactions in a number of 
ways.  Most importantly, it prohibits LISTEN/NOTIFY.  Grep for 
PreventCommandDuringRecovery() if you're interested in the scope.
                          Elvis