Alan Burlison > Solaris > Solaris::Kstat

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Module Version: 0.02   Source  

NAME ^

Solaris::Kstat - access Solaris Kstats from Perl

SYNOPSIS ^

   use Solaris::Kstat;
   my $kstat = Solaris::Kstat->new();
   my ($usr1, $sys1, $wio1, $idle1) =
      @{$kstat->{cpu_stat}{0}{cpu_stat0}}{qw(user kernel wait idle)};
   print("usr sys wio idle\n");
   while (1)
      {
      sleep 5;
      if ($kstat->update()) { print("Configuration changed\n"); }
      my ($usr2, $sys2, $wio2, $idle2) =
         @{$kstat->{cpu_stat}{0}{cpu_stat0}}{qw(user kernel wait idle)};
      printf(" %.2d  %.2d  %.2d  %.2d\n",
             ($usr2 - $usr1) / 5, ($sys2 - $sys1) / 5,
             ($wio2 - $wio1) / 5, ($idle2 - $idle1) / 5);
      $usr1 = $usr2; $sys1 = $sys2; $wio1 = $wio2; $idle1 = $idle2;
      }

DESCRIPTION ^

This module provides a tied hash interface to the Solaris kstats library. The kstats library allows you to get access to all the stats used by sar, iostat, vmstat etc, plus a lot of others that aren't accessible through the usual utilities.

Solaris categorises statistics using a 3-part key - module, instance and name. For example, the root disk stats can be found under sd.0.sd0, and the cpu statistics can be found under cpu_stat.0.cpu_stat0, as in the above example. The method Solaris::Kstats-new()> creates a new 3-layer tree of perl hashes with exactly the same structure - i.e. the stats for disk 0 can be accessed as $ks-{sd}{0}{sd0}>. The bottom (4th) layer is a tied hash used to hold the individual statistics values for a particular system resource.

Creating a Solaris::Kstat object doesn't actually read all the possible statistics in, as this would be horribly slow and inefficient. Instead it creates a 3-layer structure as described above, and only reads in the individual statistics as you reference them. For example, accessing $ks-{sd}{0}{sd0}{reads} will read in all the statistics for sd0, including writes, bytes read/written, service times etc. Once you have accessed a bottom level statitics value, calling $ks->update() will automatically update all the individual values of any statistics that you have accessed.

Note that there are two values per bottom-level hash that can be read without causing the full set of statistics to be read from the kernel. These are "class" which is the kstat class of the statistics and "crtime" which is the time that the kstat was created. See kstat(3K) for full details of these fields.

PROBLEMS WITH 64-BIT VALUES ^

Several of the statistics returned by the Solaris kstat mechanism are stored as 64-bit integer values. Perl doesn't fully support 64-bit integers (yet), so a workaround had to be found to allow 64-bit values to be stored within Perl. There are two classes of 64-bit value that have to be dealt with:

64-bit intervals and times

These are the crtime and snaptime fields of all the statistics hashes, and the wtime, wlentime, wlastupdate, rtime, rlentime and rlastupdate fields of the kstat disk statistics structures . These are expressed by the Solaris kstats library in nanoseconds. If these values are stored in a 32-bit integer they will wrap after about 4 seconds, so this is obviously not a useful thing to do. The other alternative is to store the values as floating-point numbers, which on both the Sparc & Intel architectures offer ~53 bits of precision. I have therefore decided to save all 64-bit intervals and timers as floating-point values expressed in seconds.

64-bit counters

Again, it is not useful to store these values as 32-bit values. However, as noted above floating-point values offer 53 bits of precision. Accordingly, all 64-bit counters are stored as floating-point values.

METHODS ^

new()

Create a new kstat statistics hierarchy and return a reference to the top-level hash. Use it like any normal hash to access the statistics.

refresh()

Update all the ststistics that have been accessed so far. Note that as the statistics are stored in a tied hash you can't use references to members of the hash, e.g. my $ref = \$ks-{sd}{0}{sd0}{reads}> followed by print("$$ref\n");, as the reference gets a copy of the value and won't be updated by refresh().

CAVEATS ^

Due to several bugs in Perl 5.004_04, this module won't work with that verison of Perl - Sorry. Use 5.005_02 or above, or 5.004_05 when it is available.

See the warning above about 64-bit values. Don't forget that hires times are stored in seconds, not nanoseconds.

See the warning above about references.

This isn't a tutorial on Solaris statistics and tuning - please refer to the book below.

AUTHOR ^

Alan Burlison, <Alan.Burlison@uk.sun.com>

SEE ALSO ^

perl(1), kstat(3K), kstat_open(3K), kstat_close(3K), kstat_read(3K), kstat_chain_update(3K).

"Sun Performance And Tuning - Java And The Internet" 2nd ed. by Adrian Cockroft and Richard Pettit - ISBN 0-13-095249-4. This explains what most of the individual statistics actually mean.

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