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

From: Elvis Pranskevichus <elprans(at)gmail(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.
Date: 2017-03-23 12:47:27
Message-ID: 1594731.2YIqSPIdmk@hammer.magicstack.net
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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

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