I was trying to figure how to set the log directory using a parameter in the connection string. Short answer is that you can't.
But you can using the DSN settings.
I was under the impression that going DSN-less and using the parameters on the connection string, we were free from the effects of the DSN settings.
That's not true.
The DSN settings become the default values, overridden by anything in the connection string.
So you can set default values in the DSN dialog, or you can set them in the registry.
----- ODBCLoggingOn.reg ------
[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\ODBC\ODBCINST.INI\PostgreSQL Unicode]
"Debug"="1"
"Logdir"="c:\\temp"
------------------------------------------
In the process I documented all the settings and their abbreviations in a spreadsheet. I'll post that to the docs mailing list.