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
