Connections hang if the database limit max_size is overtaken

[fluca1978]

While inspecting #456 I found this behavior that applies also to master branch 40acff635d16e00eac08bf5307efdabc03ee13cd:

% pgagroal-cli conf get max_connections
15

% pgagroal-cli conf get limit.pgbench.max_size
12

% pgagroal-cli conf get limit.pgbench.min_size
5

so the system is allowing 15 max connections and 12 are possible at max against the pgbench database. Every run with a number of client less than 12 (pgbench max connections) works:

% time /usr/pgsql-16/bin/pgbench -c 5 -n  -T 60 -h localhost -p 54322 -U pgbench pgbench
...
/usr/pgsql-16/bin/pgbench -c 5 -n -T 60 -h localhost -p 54322 -U pgbench   0.11s user 0.19s system 0% cpu 1:01.39 total

% time /usr/pgsql-16/bin/pgbench -c 10 -n  -T 60 -h localhost -p 54322 -U pgbench pgbench
...
/usr/pgsql-16/bin/pgbench -c 10 -n -T 60 -h localhost -p 54322 -U pgbench   0.12s user 0.27s system 0% cpu 1:00.53 total

% time /usr/pgsql-16/bin/pgbench -c 12 -n  -T 60 -h localhost -p 54322 -U pgbench pgbench
...
/usr/pgsql-16/bin/pgbench -c 12 -n -T 60 -h localhost -p 54322 -U pgbench   0.12s user 0.27s system 0% cpu 1:00.66 total

then when the number of clients is greater than max connections for the database, the system seems to hang the connections and the running never ends:

% time /usr/pgsql-16/bin/pgbench -c 13 -n  -T 60 -h localhost -p 54322 -U pgbench pgbench
pgbench (16.4)
^C
/usr/pgsql-16/bin/pgbench -c 13 -n -T 60 -h localhost -p 54322 -U pgbench   0.00s user 0.01s system 0% cpu 1:07.47 total


% time /usr/pgsql-16/bin/pgbench -c 15 -n  -T 60 -h localhost -p 54322 -U pgbench pgbench
pgbench (16.4)
^C
/usr/pgsql-16/bin/pgbench -c 15 -n -T 60 -h localhost -p 54322 -U pgbench   0.00s user 0.01s system 0% cpu 3:57.05 total

in the meantime, observing the status reports the connections to be in replica mode:

% pgagroal-cli status
Status:              Running
Active connections:  12
Total connections:   13
Max connections:     15
[luca@rachel]~% pgagroal-cli status details
Status:              Running
Active connections:  12
Total connections:   13
Max connections:     15
---------------------
Server:              rachel
Host:                127.0.0.1
Port:                5432
State:               Primary
---------------------
Database:            pgbench
Username:            pgbench
Active connections:  12
Max connections:     12
Initial connections: 5
Min connections:     5
---------------------
Database:            testdb
Username:            luca
Active connections:  0
Max connections:     2
Initial connections: 1
Min connections:     1
---------------------
Connection    1:     Replica         2024-09-23 17:19:59 165147 15     pgbench pgbench pgbench
Connection    2:     Replica         2024-09-23 17:19:59 165148 16     pgbench pgbench pgbench
Connection    3:     Replica         2024-09-23 17:19:59 165149 17     pgbench pgbench pgbench
Connection    4:     Replica         2024-09-23 17:19:59 165150 18     pgbench pgbench pgbench
Connection    5:     Replica         2024-09-23 17:19:59 165151 19     pgbench pgbench pgbench
Connection    6:     Primary         2024-09-23 17:19:58        20     luca testdb 
Connection    7:     Replica         2024-09-23 17:19:59 165152 5      pgbench pgbench pgbench
Connection    8:     Replica         2024-09-23 17:19:59 165154 5      pgbench pgbench pgbench
Connection    9:     Replica         2024-09-23 17:19:59 165156 5      pgbench pgbench pgbench
Connection   10:     Replica         2024-09-23 17:19:59 165158 5      pgbench pgbench pgbench
Connection   11:     Replica         2024-09-23 17:19:59 165160 5      pgbench pgbench pgbench
Connection   12:     Replica         2024-09-23 17:19:59 165162 5      pgbench pgbench pgbench
Connection   13:     Replica         2024-09-23 17:19:59 165164 5      pgbench pgbench pgbench
Connection   14:     Not init                                            
Connection   15:     Not init