Re: row filtering for logical replication

Hi,

I see no one responded to this important part of my review so far:

On 9/23/21 2:33 PM, Tomas Vondra wrote:
> 3) create_subscription.sgml
> 
>      <literal>WHERE</literal> clauses, rows must satisfy all expressions
>      to be copied. If the subscriber is a
> 
> I'm rather skeptical about the principle that all expressions have to 
> match - I'd have expected exactly the opposite behavior, actually.
> 
> I see a subscription as "a union of all publications". Imagine for 
> example you have a data set for all customers, and you create a 
> publication for different parts of the world, like
> 
>    CREATE PUBLICATION customers_france
>       FOR TABLE customers WHERE (country = 'France');
> 
>    CREATE PUBLICATION customers_germany
>       FOR TABLE customers WHERE (country = 'Germany');
> 
>    CREATE PUBLICATION customers_usa
>       FOR TABLE customers WHERE (country = 'USA');
> 
> and now you want to subscribe to multiple publications, because you want 
> to replicate data for multiple countries (e.g. you want EU countries). 
> But if you do
> 
>    CREATE SUBSCRIPTION customers_eu
>           PUBLICATION customers_france, customers_germany;
> 
> then you won't get anything, because each customer belongs to just a 
> single country. Yes, I could create multiple individual subscriptions, 
> one for each country, but that's inefficient and may have a different 
> set of issues (e.g. keeping them in sync when a customer moves between 
> countries).
> 
> I might have missed something, but I haven't found any explanation why 
> the requirement to satisfy all expressions is the right choice.
> 
> IMHO this should be 'satisfies at least one expression' i.e. we should 
> connect the expressions by OR, not AND.

Am I the only one finding the current behavior strange? What's the 
reasoning supporting the current approach?


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company