On 8/20/2004 10:08 AM, Jeremiah Jahn wrote:

> On Thu, 2004-08-19 at 14:41, Jan Wieck wrote:
>> On 8/19/2004 3:36 PM, Jeremiah Jahn wrote:
>> 
>> > If you could, wouldn't that fix the problem? So, would it be worthwhile
>> > to be able to put a trigger on at least the LO table, maybe even other
>> > system tables (for schema replication). I assume that it's a performance
>> > issue that has prevented this before.
>> 
>> No. The issue is that system catalog updates most of the time don't go  
>> through the executor, but call heap_insert(), heap_update and 
>> heap_delete() directly. The trigger mechanism is in the executor.
> 
> 'System catalog' updates refers to schema changes right, and not lo
> updates? If that is the case, then what prevents adding a hook to enable
> triggers on the lo table. As for changes to the schema , why not just
> push them through the executor all of the time, instead of some of the
> time?

Take a look at src/backend/storage/large_object/inv_api.c and then come 
up with a design how to add trigger capabilities to that. This design 
should preferrably include a way to create/modify/delete large objects 
through the SQL querylanguage or it would impose a roadblock for one of 
the future plans for Slony-I.

We have some time for the whole design because this is a feature that 
cannot be added by working on Slony alone. It needs modifications in the 
PostgreSQL backend. Since we will not get those into any existing, 
released version of PostgreSQL, this feature would be restricted to 
PostgreSQL 8.1 and newer. 8.0 is already in feature freeze.


Jan

> 
>> 
>> 
>> Jan
>> 
>> > 
>> > -jj-  
>> > 
>> > On Thu, 2004-08-19 at 13:29, Doug McNaught wrote:
>> >> Jeremiah Jahn <jeremiah at cs.earlham.edu> writes:
>> >> 
>> >> > So it's not possible to just trigger off of the pg_large_object table?
>> >> 
>> >> No, you can't put triggers on system tables.
>> >> 
>> >> -Doug


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