Re: [HACKERS] For review: Server instrumentation patch

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > What I can imagine making things very easy is a readonly GUC that returns
> > the current log file name.
>
> ... which unfortunately is not going to happen since the backends can't
> see inside the syslogger process to know what it's doing.

That's a shame.

> ATM I think the best you can do is look for the newest mod date among
> the files in the log directory.

I guess, but then you have the pattern problem, especially if you are
putting things in /var/log where there are other log files too.

One idea would be to implement pg_ls_logdir() as a system view, and then
build a GUC on that, but I am not sure that is possible.  Here is an
updated version of the query that also checks the file extension:

    SELECT pg_ls_dir
    FROM    (
            SELECT pg_ls_dir(t1.setting)
            FROM    (SELECT setting FROM pg_settings
            WHERE NAME = 'log_directory') AS t1
        ) AS t2,
        (SELECT setting FROM pg_settings
         WHERE NAME = 'log_filename') AS t3
    WHERE  t2.pg_ls_dir LIKE regexp_replace(t3.setting, '%.*', '') ||
        '%' || regexp_replace(t3.setting, '.*\\.', '.') ;

                pg_ls_dir
    ----------------------------------
     postgresql-2005-08-12_211251.log
     postgresql-2005-08-13_000000.log
    (2 rows)

Also, do we have a way to return columns from a system-installed
function?  I really don't like that pg_stat_file() to returns a record
rather than named columns.  How do I even access the individual record
values?

    test=> select pg_stat_file('.');
                                   pg_stat_file
    ---------------------------------------------------------------------------

     (512,"2005-08-12 21:13:01","2005-08-13 07:08:54","2005-08-12 21:13:01",t)
    (1 row)

    test=> select pg_stat_file('.')[1];
    ERROR:  syntax error at or near "[" at character 25

We have system _tables_ that return columns, like pg_settings, but of
course that doesn't take any arguments, just a WHERE clause, so that
wouldn't work here.

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