Re: max_connections different between primary and standby: is it possible?

Hi,

On Thu, Feb 03, 2022 at 10:36:37AM +0100, Luca Ferrari wrote:
> Hi all,
> running PostgreSQL 14, physical replication with slot, after changing
> (increasing) the max_connections on the primary, I had this message at
> a restart from the standby:
>
> DETAIL: max_connections = 100 is a lower setting than on the primary
> server, where its value was 300.
>
> and the standby does not start until I raise also its max_connections.
> Why is PostgreSQL requiring the max_connections to be aligned between
> the primary and the standby?

The value needs to be at least equal as the value on the primary node, but it
can be bigger.

That's because the standby needs to have enough resources to replay the
activity from the primary, including some heavyweight locks acquisition, and
the number of locks you can hold at one time is partially based on
max_connections.