Re: Add %r substitution for psql prompts to show recovery status

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От Alexander Korotkov
Тема Re: Add %r substitution for psql prompts to show recovery status
Дата
Msg-id CAPpHfduiDiHwC6gcJCr=f=2c62XBnvbCr-6MVLMBagw8mQ7X5Q@mail.gmail.com
обсуждение исходный текст
Ответ на Re: Add %r substitution for psql prompts to show recovery status  (Tatsuo Ishii <ishii@sraoss.co.jp>)
Ответы Re: Add %r substitution for psql prompts to show recovery status  (Tatsuo Ishii <ishii@sraoss.co.jp>)
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Дерево обсуждения
On Fri, Dec 8, 2017 at 3:54 AM, Tatsuo Ishii <ishii@sraoss.co.jp> wrote:
> On Wed, Dec 6, 2017 at 9:19 PM, Ian Barwick <ian.barwick@2ndquadrant.com> wrote:
>> Note this substitution sends a "pg_is_in_recovery()" query to the server
>> each time it's encountered; unless there's something I'm overlooking I
>> think that's the only reliable way to determine current recovery status.
>
> That seems kinda painful.
>
> And what happens in an aborted transaction?

Yeah. I think we need some from help backend for this. For example, a
parameter status message can be used here.  If PostgreSQL moves to the
recovery state or vice versa, PostgreSQL sends the parameter status
message to frontend.

If we would use parameter status messages, then can we handle compatibility correctly?  So that new psql can work with old backend without errors (and without recovery status display, for sure), and old psql can work with new backend without errors.

Because seeing recovery status in psql prompt is very neat.  But execution of extra query each time doesn't seem like reasonable price for it...

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company 

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