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'\" te
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.TH KSTAT 3PERL "Jul 21, 2005"
.SH NAME
Kstat \- Perl tied hash interface to the kstat facility
.SH SYNOPSIS
.LP
.nf
use Sun::Solaris::Kstat;

Sun::Solaris::Kstat->new();
Sun::Solaris::Kstat->update();
Sun::Solaris::Kstat->{module}{instance}{name}{statistic}
.fi

.SH DESCRIPTION
.sp
.LP
Kernel statistics are categorized using a 3-part key consisting of the module,
the instance, and the statistic name. For example, CPU information can be found
under \fBcpu_stat:0:cpu_stat0\fR, as in the above example. The method
\fBSun::Solaris::Kstat\fR\(->\fBnew()\fR creates a new 3-layer tree of Perl
hashes with the same structure; that is, the statistic for CPU 0 can be
accessed as \fB$ks\(->{cpu_stat}{0}{cpu_stat0}\fR. The fourth and lowest layer
is a tied hash used to hold the individual statistics values for a particular
system resource.
.sp
.LP
For performance reasons, the creation of a \fBSun::Solaris::Kstat\fR object is
not accompanied by a following read of all possible statistics. Instead, the
3-layer structure described above is created, but reads of a statistic's values
are done only when referenced. For example, accessing
\fB$ks\(->{cpu_stat}{0}{cpu_stat0}{syscall}\fR will read in all the statistics
for CPU 0, including user, system, and wait times, and the other CPU
statistics, as well as the number of system call entries. Once you have
accessed a lowest level statistics value, calling \fB$ks\fR\(->\fBupdate()\fR
will automatically update all the individual values of any statistics you have
accessed.
.sp
.LP
There are two values of the lowest-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 \fBkstat\fR class of the statistics, and "crtime"n, which is the time
that the kstat was created. See \fBkstat\fR(3KSTAT) for full details of these
fields.
.SS "Methods"
.sp
.ne 2
.na
\fB\fBnew()\fR\fR
.ad
.RS 12n
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.
.RE

.sp
.ne 2
.na
\fB\fBupdate()\fR\fR
.ad
.RS 12n
Update all the statistics that have been accessed so far.  In scalar context,
\fBupdate()\fR returns 1 if the \fBkstat\fR structure has changed, and 0
otherwise. In list context, \fBupdate()\fR returns references to two arrays:
the first holds the keys of any kstats that have been added, and the second
holds the keys of any kstats that have been deleted. Each key will be returned
in the form "\fBmodule\fR:\fBinstance\fR:\fBname\fR".
.RE

.SH EXAMPLES
.LP
\fBExample 1 \fRSun::Solaris::Kstat example
.sp
.in +2
.nf
use Sun::Solaris::Kstat;

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

.SH SEE ALSO
.sp
.LP
\fBperl\fR(1), \fBkstat\fR(8), \fBkstat\fR(3KSTAT),
\fBkstat_chain_update\fR(3KSTAT), \fBkstat_close\fR(3KSTAT),
\fBkstat_open\fR(3KSTAT), \fBkstat_read\fR(3KSTAT)
.SH NOTES
.sp
.LP
As the statistics are stored in a tied hash, taking additional references of
members of the hash, such as
.sp
.in +2
.nf
my $ref = \eks->{cpu_stat}{0}{cpu_stat0}{syscall};
print("$$ref\en");
.fi
.in -2

.sp
.LP
will be recorded as a hold on that statistic's value, preventing it from being
updated by \fBrefresh()\fR. Copy the values explicitly if persistence is
necessary.
.sp
.LP
Several of the statistics provided by the \fBkstat\fR facility are stored as
64-bit integer values. Perl 5 does not yet internally support 64-bit integers,
so these values are approximated in this module. There are two classes of
64-bit value to be dealt with:
.sp
.ne 2
.na
\fB64-bit intervals and times\fR
.ad
.RS 30n
These are the \fBcrtime\fR and \fBsnaptime\fR fields of all the statistics
hashes, and the \fBwtime\fR, \fBwlentime\fR, \fBwlastupdate\fR, \fBrtime\fR,
\fBrlentime\fR and \fBrlastupdate\fR fields of the \fBkstat\fR I/O statistics
structures.  These are measured by the \fBkstat\fR facility in nanoseconds,
meaning that a 32-bit value would represent approximately 4 seconds. The
alternative is to store the values as floating-point numbers, which offer
approximately 53 bits of  precision on present hardware. 64-bit intervals and
timers as floating point values expressed in seconds, meaning that time-related
kstats are being rounded to approximately microsecond resolution.
.RE

.sp
.ne 2
.na
\fB64-bit counters\fR
.ad
.RS 30n
It is not useful to store these values as 32-bit values. As noted above,
floating-point values offer 53 bits of precision. Accordingly, all 64-bit
counters are stored as floating-point values.
.RE