On 3/10/2005 3:32 PM, David Parker wrote:

> This is not strictly a slony question, but it has to do with some slony
> procedure code I would like to emulate... I have a data broadcasting
> functionality that is layered on top of a slony installation that I use
> to get data replicated out to nodes from a central location without
> those nodes having to be part of this slony cluster (all nodes are
> actually pairs, Active/Standby, and we are using our trusty slony to
> maintain data redundancy between them).
>  
> When a node subscribes I want to do an initial delete/copy of a set of
> tables the way slony does, but I need to get around FK constraints. My
> understanding of the altertableforreplication procedure is:
>  
>      - for each table that needs to be altered and has
> triggers/constraints
>             -update the pg_triggers record for each trigger to point to
> the table's primary key object (maintained
>             in the sl_table table)
>             - update the record for the current table in pg_class to
> decrement the reltriggers column
>  
> And then the restore reverses this process.
>  
> The procedure also disables rules - are both of these steps necessary to
> "disable" constraints, or is it sufficient to just point the triggers
> away?
>  
> I'm not sure I can implement this the same way, because I don't
> necessarily have a primary key to substitute with on all of the target
> tables, but I can build in some other kind of table to my schema to help
> track these relations.
>  
> But first, am I understanding correctly the way altertableforreplication
> works?!

This is precisely how it is done. The fact that the pg_trigger rows do 
not contain the relations OID any more is the key point here. That 
causes the triggers not to be loaded into the relation descriptor (on 
heap_open()) and therefore not being fired, or even known by the executor.

Rewrite rules are just another mechanism that can cause side effects on 
INSERT/UPDATE/DELETE. If you want to do a DELETE+COPY, then you better 
make sure you don't have any ON DELETE rules on those tables. COPY does 
not invoke rules.


Jan

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