On Tue, Jun 13, 2017 at 12:16:00PM -0400, Robert Haas wrote:
> It might be worth adding platform-specific code for common platforms.

All I care (which linux happily/happens to support) is maxrss; I was probably
originally interested in this while digging into an issue with hash agg.

I think it's fine to show zeros for unsupported fields; that's what getusage(2)
and time(1) do after all.

pryzbyj@pryzbyj:~$ sh -c 'command time -v find /dev' 2>&1 >/dev/null |grep -Fw 0
        User time (seconds): 0.00
        System time (seconds): 0.00
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.00
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0

> it would be a good idea to install code specific to Linux that
> displays all and only those values that are meaningful on Linux, and
> (less importantly) similarly for macOS.  Linux is such a common
> platform that reporting bogus zero values and omitting other fields
> that are actually meaningful does not seem like a very good plan.

That has the issue that it varies not just by OS but also by OS version.  For
example PG already shows context switches and FS in/out puts, but they're
nonzero only since linux 2.6 (yes, 2.4 is ancient and unsupported but still).

       ru_nvcsw (since Linux 2.6)
       ru_inblock (since Linux 2.6.22)

..and other fields are "currently unused", but maybe supported in the past or
       ru_ixrss (unmaintained)
              This field is currently unused on Linux.

Are you thinking of something like this, maybe hidden away in a separate file

#if defined(__linux__) || defined(BSD)
        appendStringInfo(&str, "!\t%ld max resident, %ld shared, %ld unshared 
data, %ld unshared stack (kB)\n", r.ru_maxrss, r.ru_ixrss, r.ru_idrss, 
#elif defined(__darwin__)
        appendStringInfo(&str, "!\t%ld max resident, %ld shared, %ld unshared 
data, %ld unshared stack (kB)\n", r.ru_maxrss/1024, r.ru_ixrss/1024, 
r.ru_idrss/1024, r.ru_isrss/1024);
#endif /* __linux__ */


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