Re: a misbehavior of partition row movement (?)

Hi Rahila,

On Wed, Feb 24, 2021 at 3:07 PM Rahila Syed <rahilasyed90(at)gmail(dot)com> wrote:
>> > I think the documentation update is missing from the patches.
>>
>> Hmm, I don't think we document the behavior that is improved by the v3
>> patches as a limitation of any existing feature, neither of foreign
>> keys referencing partitioned tables nor of the update row movement
>> feature. So maybe there's nothing in the existing documentation that
>> is to be updated.
>>
>> However, the patch does add a new error message for a case that the
>> patch doesn't handle, so maybe we could document that as a limitation.
>> Not sure if in the Notes section of the UPDATE reference page which
>> has some notes on row movement or somewhere else. Do you have
>> suggestions?
>>
> You are right, I could not find any direct explanation of the impact of row movement during
> UPDATE on a referencing table in the PostgreSQL docs.
>
> The two documents that come close are either:

Thanks for looking those up.

> 1. https://www.postgresql.org/docs/13/trigger-definition.html .
> The para starting with "If an UPDATE on a partitioned table causes a row to move to another partition"
> However, this does not describe the behaviour of internal triggers which is the focus of this patch.

The paragraph does talk about a very related topic, but, like you, I
am not very excited about adding a line here about what we're doing
with internal triggers.

> 2. Another one like you mentioned, https://www.postgresql.org/docs/11/sql-update.html
> This has explanation for row movement behaviour for partitioned table but does not explain
> any impact of such behaviour on a referencing table.
> I think it is worth adding some explanation in this document. Thus, explaining
> impact on referencing tables here, as it already describes behaviour of
> UPDATE on a partitioned table.

ISTM the description of the case that will now be prevented seems too
obscure to make into a documentation line, but I tried. Please check.

--
Amit Langote
EDB: http://www.enterprisedb.com