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

On 11 April 2017 at 09:05, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> On Tue, Apr 11, 2017 at 3:26 AM, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
> wrote:
>>
>> On Mon, Apr 10, 2017 at 5:47 PM, Magnus Hagander <magnus(at)hagander(dot)net>
>> wrote:
>> > Based on that we seem to agree here, should we add this as an open item?
>> > Clearly if we want to change this, we should do so before 10.
>>
>> This really is a new feature, so as the focus is to stabilize things I
>> think that we should not make the code more complicated because...
>
>
> The part I'm talking about is the potential adjustment of the patch that's
> already committed. That's not a new feature, that's exactly the sort of
> thing we'd want to adjust before we get to release. Because once released we
> really can't change it.

I agree if we introduce target_session_attrs it would be better to
have a complete feature in one release.

It does seem quite strange to have
target_session_attrs=read-write
but not
target_session_attrs=read-only

And it would be even better to have these session attrs as well
notify-on-promote - sent when standby is promoted
notify-on-write - sent when an xid is assigned

"notify-on-promotion" being my suggested name for the feature being
discussed here. In terms of the feature as submitted, I wonder whether
having a GUC parameter like this makes sense, but I think its ok for
us to send a protocol message, maybe a NotificationResponse, but there
isn't any material difference between those two protocol messages.

Rather than the special case code in the patch, I imagine more generic
code like this...

if (sessionInterruptPending)
ProcessSessionInterrupt();

I'm happy to work on the patch, if that's OK.

--
Simon Riggs http://www.2ndQuadrant.com/
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