On Tue, 5 Mar 2019, SAS wrote:

> Thank you for your answer.
> 
> I could easily drop some paths, and then lower the number of established connections on some
> nodes.
> 
> Could you point me to what has changed between 2.1 and 2.2 branches that causes this connections
> increase? The paths were there before the upgrade.

It has to do with the changes to how DDL is handled.
In 2.1 and earlier DDL was treated as a special type of event and was 
replicated by this event in sl_event.  There were cases where DDL and data 
could be replicated in the wrong order.

In 2.2 there is now a table specifically for DDL changes, like sl_log.  The 
DDL from this table is pulled in the correct order by the listener threads 
through the listener connection.

DDL can be submitted on any node, and for nodes that aren't providing a 
subscription there isn't a clear cascaded network route though other nodes.

For larger node setups it might be nice to have a way of designating nodes 
as 'edge only' nodes, where they can't be origin's, providers or failover 
targets and they can't accept DDL submissions.  These nodes wouldn't have to 
generate any events and so other nodes wouldn't have to listen 
for their events.  We don't currently support this though.

Hope that helps.

> Best,
> 
> --
> Dr Stéphane Schildknecht
> Contact régional PostgreSQL pour l'Europe francophone
> +33 617 11 37 42
> 
> 
>