Add more information to "connect timeout" errors: include hosts attempted, hosts skipped, timeout values

[vlsi]

If loginTimeout is less than connectTimeout * numberOfHosts, then the connect operation might fail in case the first attempted replicas take a lot of time to connect.

The error message could probably include "attempted these hosts: ..., skipped hosts ... due to loginTimeout=... reached. Consider increasing loginTimeout or decreasing connectTimeout".

[imranzaheer612]

Reproducing Error

I was able to reproduce the error. The first node here is unreachable but he second one works.

         Class.forName("org.postgresql.Driver");
         String url = "jdbc:postgresql://172.19.112.5:5334,172.19.112.6:5335/postgres";
         Properties props = new Properties();
         props.setProperty("user", "postgres");
         props.setProperty("password", "postgres");
         props.setProperty("loginTimeout", "5");

this caused generating the error.

org.postgresql.util.PSQLException: Connection attempt timed out.

Adding property of props.setProperty("connectTimeout", "1"); you can remove this error and the connection will be successfull.

Some Improvement

I tried adding more info but so far I was only able to add the loginTimeout.
In Driver.java added this piece of code

pgjdbc/pgjdbc/src/main/java/org/postgresql/Driver.java

Line 423 in 0fbd31d

throw new RuntimeException(GT.tr("Interrupted while attempting to connect."));

          throw new PSQLException(GT.tr("Connection attempt timed out. Logintimeout=: " + TimeUnit.MILLISECONDS.toSeconds(timeout) + "reached."),

Now the errors looks like

org.postgresql.util.PSQLException: Connection attempt timed out. Logintimeout: 5 reached

Some remedy to get attempted and skippedHosts

There is a local variable knownStates in openConnectionImpl we can calculate the attemptedHosts from here. But its a local variable.
If we can propagate this from ConnectionFactoryImpl.java to Driver.java we can have some more info for the error message.

pgjdbc/pgjdbc/src/main/java/org/postgresql/core/v3/ConnectionFactoryImpl.java

Line 236 in 0fbd31d

Map<HostSpec, HostStatus> knownStates = new HashMap<>();

Kindly share your thoughts.