Upgrade packages - Control Instance

Hi,

I'm looking for a way to control the way instances are restarted when
`apt upgrade` run => sometime, if there is a large number of packages to
upgrade, the instances is stopped for a long time.

In the past, I used to use start.conf with manual setting, then restart
"manually" after the upgrade, which give downtime as short as I can ;
but now, it seems that "stop" is always done, even when i disable the
systemd service (ok,it is weird to disable service and to want the
service up, I know ) => I think that the fact we can't forbid the stop
is not correct.

I know that I can hold the postgresql packages, run the big `apt
upgrade` then unhold packages and do the postgresql upgrade, but I think
it's a more complicated way to do it.

Am I miss something ?

Am I the only one disturbed by the fact that we can't forbid stop ?

regards,

-- 

Sébastien