Re: [HACKERS] UPDATE of partition key - Mailing list pgsql-hackers

On 5 June 2017 at 11:27, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Fri, Jun 2, 2017 at 4:37 PM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
>> On 2 June 2017 at 01:17, Robert Haas <robertmhaas@gmail.com> wrote:
>>> On Thu, Jun 1, 2017 at 7:41 AM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
>>>>> Regarding the trigger issue, I can't claim to have a terribly strong
>>>>> opinion on this.  I think that practically anything we do here might
>>>>> upset somebody, but probably any halfway-reasonable thing we choose to
>>>>> do will be OK for most people.  However, there seems to be a
>>>>> discrepancy between the approach that got the most votes and the one
>>>>> that is implemented by the v8 patch, so that seems like something to
>>>>> fix.
>>>>
>>>> Yes, I have started working on updating the patch to use that approach
>>>> (BR and AR update triggers on source and destination partition
>>>> respectively, instead of delete+insert) The approach taken by the
>>>> patch (BR update + delete+insert triggers) didn't require any changes
>>>> in the way ExecDelete() and ExecInsert() were called. Now we would
>>>> require to skip the delete/insert triggers, so some flags need to be
>>>> passed to these functions,
>>>>
>
> I thought you already need to pass an additional flag for special
> handling of ctid in Delete case.

Yeah that was unavoidable.

> For Insert, a new flag needs to be
> passed and need to have a check for that in few places.

For skipping delete and insert trigger, we need to include still
another flag, and checks in both ExecDelete() and ExecInsert() for
skipping both BR and AR trigger, and then in ExecUpdate(), again a
call to ExecARUpdateTriggers() before quitting.

>
>> or else have stripped down versions of
>>>> ExecDelete() and ExecInsert() which don't do other things like
>>>> RETURNING handling and firing triggers.
>>>
>>> See, that strikes me as a pretty good argument for firing the
>>> DELETE+INSERT triggers...
>>>
>>> I'm not wedded to that approach, but "what makes the code simplest?"
>>> is not a bad tiebreak, other things being equal.
>>
>> Yes, that sounds good to me.
>>
>
> I am okay if we want to go ahead with firing BR UPDATE + DELETE +
> INSERT triggers for an Update statement (when row movement happens) on
> the argument of code simplicity, but it sounds slightly odd behavior.

Ok. Will keep this behaviour that is already present in the patch. I
myself also feel that code simplicity can be used as a tie-breaker if
a single behaviour  cannot be agreed upon that completely satisfies
all aspects.

>
>> But I think we want to wait for other's
>> opinion because it is quite understandable that two triggers firing on
>> the same partition sounds odd.
>>
>
> Yeah, but I think we have to rely on docs in this case as behavior is
> not intuitive.

Agreed. The doc changes in the patch already has explained in detail
this behaviour.

>
> --
> With Regards,
> Amit Kapila.
> EnterpriseDB: http://www.enterprisedb.com



-- 
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company