El Jueves, 17 de Febrero de 2005 19:17, Jan Wieck escribi?:
> On 2/17/2005 2:08 PM, Andrew Sullivan wrote:
> > On Thu, Feb 17, 2005 at 01:17:16PM -0500, Jan Wieck wrote:
> >> On 2/16/2005 6:46 AM, Andrew Sullivan wrote:
> >> >Yes.
> >>
> >> Actually not exactly. The query executed on the subscriber would be
> >>
> >>     update example_table set key = '4' where key = '4';
> >>
> >> The slony log trigger filters out unchanged columns. If that results in
> >> no column change at all (empty SET clause in the update), it adds the
> >> first key column so that the update becomes valid SQL.
> >
> > Sorry, I should have been clearer.  Jan is of course right that the
> > trigger filters unchanged columns; but the OP wanted to know if it
> > filters out queries which do no work or have no effect.  The answer
> > to that, as far as I know, is no, and Jan's example above illustrates
> > it.
>
> We (my stomach and I) had been thinking about filtering out NOOP's
> entirely. But that would be in conflict with subscriber side enabled
> user triggers, which do get called even if the update does in fact
> nothing like the above example.
>
> The solution would be another attribute on sl_table which is used to
> define another argument for the log trigger which controls the filter.

So, if this feature is implemented, it would be easy to make Slony skip 
"unnecessary" statements. If, in addition, the mechanism that avoid you to 
update a subscribed table (What is it? A simple trigger?) is disabled...
would it be possible to set a double (symetric) master-slave relation between 
the tables to have a "multimaster" (with only two implied databases) system?

I mean, Table1 in Host1 is a master of Table1 in Host2 and Table1 in Host2 is 
a master of Table1 in Host1. Of course, there is not conflict resolution at 
all but, at least, there are not infinite loops of updates (if unnecessary 
updates are skipped) unless when a same record is updated in both databases 
"simultaneously". In fact, it's not a real multimaster system because there 
are a lot of situations that must be explicitly avoided by the applications 
using the databases but...

Would it work? Would it explode?

Greetings
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