RE: libpq debug log

Hi Jim Doty san,

Thank you for review! I'm sorry my late reply...

> Initial Pass
> ============
> 
> + Patch applies
> + Patch builds
> + Patch behaves as described in the thread
Thank you for your check.

> When I set a path for `PGLOGDIR` that didn't exist or was not write-able,
> the patch writes no files, and does not alert the user that no files are being
> written.
I understand. I think it means that it is necessary to confirm how the setting is going well. 
There is no warning method when connection string or the environment variable is wrong.

So I added following document:
+   If the setting of the file path by the connection string or the environment variable is
+   incorrect, the log file is not created in the intended location.
+   The maximum log file size you set is output to the beginning of the file, so you can check it.
And I added the process. Please see my v2 patch.

> Performance
> ===========
> 
> I ran two permutations of make check, one with the patch applied but not
> activated, and the other with with the files being written to disk. Each
> permutation was run ten times, and the stats are below (times are in
> seconds):
> 
>               min  max  median  mean
> not logging  50.4 57.6    53.3  53.4
>     logging  58.3 77.7    65.0  65.8
Thank you for your measurement. 
I'm thinking about adding a logging level so that only the necessary information can be printed by default. It was
pointedout by Haribabu san's e-mail.
 
This minimizes the impact of logging on performance.

Regards,
Aya Iwata