Thread: [HACKERS] Why forcing Hot_standby_feedback to be enabled when creating alogical decoding slot on standby

On Mon, Jun 12, 2017 at 3:16 PM, sanyam jain <sanyamjain22@live.in> wrote:
> I have created a logical decoding slot on a standby but i haven't enabled
> Hot_standby_feedback.What are the test cases where this setup will fail?

hot_standby_feedback needs to be enabled at all times in logical
decoding so as the node does not remove rows that are still needed for
the decoding, and a VACUUM passing by with a minimal xmin too high
would cause inconsistent decoded data.
-- 
Michael

Hi,

On 2017-06-12 06:16:50 +0000, sanyam jain wrote:
> I have created a logical decoding slot on a standby but i haven't enabled Hot_standby_feedback.What are the test
caseswhere this setup will fail?
 

Creating logic slots on the standby is not supported...  It'll simply
currently not work correctly, even if you circumvent the protections
(like not being able to create one on a standby).

- Andres

Hi,

On 2017-06-16 06:31:03 +0000, sanyam jain wrote:
> Isn't XLogRecord carries full information to be decoded in itself?If so a VACCUM should not be a problem in
decoding?

First: Please don't full quote emails.
Secondly: You've not actually explained what you want to do, nor what
your precise question itself is. Nor why Michael or my answer wasn't
sufficient.

Logicla decoding looks at the catalogs for metadata - otherwise the WAL
would need to contain a lot more information and thus be more voluminous
- so the records do *not* contain the "full information".

Please start at the beginning and explain what you're trying to do
(since you apparently did some hacking to get a slot on a standby) and
what you're trying to achieve, instead of one-sentence questions.

- Andres