On 2/16/2005 6:46 AM, Andrew Sullivan wrote:

> On Wed, Feb 16, 2005 at 10:12:53AM +0000, ancorgs at banot.net wrote:
>> 1) In the master node this query is performed:
>>   UPDATE Example_table SET name = 'juan' WHERE key = '4'
>> 
>>   It's the same query performed in the slave node?
>>   (Note that, in fact, it's not necessary)
> 
> Yes.  In fact, erserver used to try to avoid propagating such things
> to the slave, and the cost wasn't worth the benefit: the overhead was
> so great that it killed you.

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.


Jan

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