libpq debug log

Hi,

I'm going to propose libpq debug log for analysis of queries on the application side.
I think that it is useful to determine whether the cause is on the application side or the server side when a slow query occurs.

The provided information is "date and time" at which execution of processing is started, "query", "application side processing", which is picked up information from PQtrace(), and "connection id", which is for uniquely identifying the connection.

To collect the log, set the connection string or environment variable.
- logdir or PGLOGDIR : directory where log file written
- logsize or PGLOGSIZE : maximum log size

What do you think about this? Do you think that such feature is necessary?

Regards,
Aya Iwata