Re: row filtering for logical replication

On Thu, Sep 23, 2021 at 10:33 PM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> 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.
>

Fixed in V40 [1]

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[1] https://www.postgresql.org/message-id/CAHut%2BPv-D4rQseRO_OzfEz2dQsTKEnKjBCET9Z-iJppyT1XNMQ%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia