Re: [Postgres-xc-developers] Shippability of statement triggers

[Ashutosh B. <ash...@en...>]

On Fri, May 10, 2013 at 5:59 PM, Michael Paquier
<mic...@gm...>wrote:

>
>
>
> On Fri, May 10, 2013 at 2:59 PM, Ashutosh Bapat <
> ash...@en...> wrote:
>
>> Can you comment on this, since you are the one who implemented statement
>> triggers?
>>
> About the shippability of triggers, here is some food for brain:
> http://michael.otacoo.com/postgresql-2/triggers-in-a-cluster-database/
>
> In short, a trigger can be fired on a remote node only if:
> - the query that triggered it is FQSed
>

That's busted, and hence this whole mail tread.


> - the fired procedure is immutable. There might be cases where a trigger
> with a stable procedure could be shippable but this would be dangerous...
> There are already some APIs I implemented that you can use if they are not
> used already (trigger.c or something in the shippability APIs of the
> optimizer I don't recall precisely).
>

Unfortunately those APIs are found to be heavily erroneous and Amit is
currently working on writing correct APIs.


>
> Just knowing that 99% of triggers do not use immutable functions is enough
> to shoot all the triggers on Coordinators, you will be bad performance for
> row triggers but if you don't do that data consistency is badly endangered.
> However for correctness you should open the open to immutable triggers
> being shippable.
> --
> Michael
>



-- 
Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Postgres Database Company