Re: Logical replication existing data copy

On 19/12/16 18:25, Peter Eisentraut wrote:
> On 12/19/16 4:30 AM, Petr Jelinek wrote:
>> So existing table data can be copied once subscription is created, but
>> also new tables can be added and their data copied. This is where the
>> REFRESH PUBLICATION comes into play. Adding table to publication does
>> not make it automatically replicated by the subscription as the
>> subscription does not have tracking info for that table. So to add new
>> table user must call ALTER SUBSCRIPTION ... REFRESH PUBLICATION on
>> subscriber otherwise the data won't be replicated.
>
> Couldn't the subscriber automatically add tracking info when apply
> stream data arrives for a relation it has not seen before?
>

Sure, but it has many caveats:
- what if the table does not exist
- what it if exists and already has data
- what if the table is rarely written to

We can't control any of that until we have DDL replication/automatic
structure dumping. Once we have those, we can add options to control
default behavior per subscriber, but with current feature set, anything
that does not require user action will behave non-deterministically
which is usually confusing.

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services