Re: [PATCH] improve the pg_upgrade error message

> The admin might fix DB123, restart their upgrade procedure, spend 5 or 15
> minutes with that, only to have it then fail on DB1234.
>

Agree with this observation.

Here is a patch that writes the list of all the databases other than
template0
that are having their pg_database.datallowconn to false in a file. Similar
approach is seen in other functions like check_for_data_types_usage(),
check_for_data_types_usage() etc. Thanks Suraj Kharage for the offline
suggestion.

PFA patch.

For experiment, here is how it turns out after the fix.

postgres=# update pg_database set datallowconn='false' where datname in
('mydb', 'mydb1', 'mydb2');
UPDATE 3

$ pg_upgrade -d /tmp/v96/data -D /tmp/v13/data -b $HOME/v96/install/bin -B
$HOME/v13/install/bin
Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok
Checking database user is the install user                  ok
Checking database connection settings                       fatal

All non-template0 databases must allow connections, i.e. their
pg_database.datallowconn must be true. Your installation contains
non-template0 databases with their pg_database.datallowconn set to
false. Consider allowing connection for all non-template0 databases
using:
    UPDATE pg_catalog.pg_database SET datallowconn='true' WHERE datname NOT
LIKE 'template0';
A list of databases with the problem is given in the file:
    databases_with_datallowconn_false.txt

Failure, exiting

$ cat databases_with_datallowconn_false.txt
mydb
mydb1
mydb2


Regards,
Jeevan Ladhe