Issue type:

[ ] question
[x] bug report
[ ] feature request
[ ] documentation issue

Database system/driver:

[ ] cordova
[ ] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[x] postgres
[ ] cockroachdb
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[ x] latest
[ ] @next
[ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

PostgresQueryRunner is not handling idle connection errors, thus all the connection related errors are unhandled and process usually dies with unexpected error.

    at Connection.<anonymous> (/Users/jaan/Projects/typeormtest/node_modules/pg/lib/client.js:275:71)
    at Object.onceWrapper (events.js:417:28)
    at Connection.emit (events.js:311:20)
    at Connection.EventEmitter.emit (domain.js:482:12)
    at Socket.<anonymous> (/Users/jaan/Projects/typeormtest/node_modules/pg/lib/connection.js:126:10)
    at Socket.emit (events.js:323:22)
    at Socket.EventEmitter.emit (domain.js:482:12)
    at endReadableNT (_stream_readable.js:1204:12)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)

It is not quite obvious when reading node-postgres documentation, but it is there under https://node-postgres.com/api/client - 'event' section. The client returned from pool.connect() must handle on('error') events because this is where idle connection error are returned. It seems pool.on('error') is not enough.

Also if you look node-postgres pool.query() function you can see they are handling on('error') and client.query() errors.

Now that said, the issue is made worse by a bug in in node-postgres - when idle connection error handler is not attached, client.query() does not actually throw at all brianc/node-postgres#2191 .

Of course if this issue is fixed without fixing #5112 the connection would be returned to the pool until the pool fills with broken connections.

Small example to play with, if you stop postgres, the exceptions are not caught and process dies :
https://gist.github.com/joras/03bf07a7eb0ab0f7bc755f15b510b432