[rrd-users] Questions from a new user...

[David Ball]

  I've never used RRDp.  Is it just me, or does your line #9  have an
extra $ in it?  If you're setting

$answer=RRDp::read;

   then shouldn't you be printing $answer and not $$answer?  Might
explain why Perl is saying $$answer is not defined.

David

On 7/19/07, Mark Seger <Mark.Seger at hp.com> wrote:
> I'm new to rrd and so am trying some very basic things.  I've been able
> to create an rrd database - real easy! and have even been able to write
> data to it using commands like:
>
> rrdtool update collectl.rrd 1184857063:0:100:100:0:7776:7776:0:1926:1926
>
> all works as advertised.  Now I want to get fancy and try using RRDp to
> handle the work because I found for a large number of updates the above
> method is pretty slow and I'm sure (or at least hoping) a lot has to do
> with the starting of the rrdtool image every time.
>
> so I now have a perl script that looks like this, which is right out of
> the man page:
>
> #!/usr/bin/perl -w
>
> use lib "/usr/local/rrdtool-1.2.23/lib/perl/5.8.5";
> use RRDp;
>
> RRDp::start "/usr/local/rrdtool-1.2.23/bin/rrdtool";
> RRDp::cmd ("update", "collectl.rrd", "1184857053:0:98:98:0:0:0:0:0:0");
> $answer=RRDp::read;
> print "$$answer\n";
>
> The only thing is I get an initialized variable when I try to print
> $$answer as you can see from the following:
>
> [root at poker rrd]# ./test.pl
> Use of uninitialized value in concatenation (.) or string at ./test.pl
> line 9.
>
> If I go into the RRDp.pm and uncomment the print statement at line 162,
> I see it set to a value of OK  which would cause the 'else' clause right
> below it to execute which sees there is no error and so returns
> '$buffer'.  Unfortunately $buffer is not defined and so I'm getting the
> uninit var back in my script.  Or am I missing something?
>
> Here's what it looks like with that print statement uncommented as well
> as a print statement I inserted to print the contents of $buffer:
>
> [root at poker rrd]# ./test.pl
> OK u:0.00 s:0.00 r:0.08
> Use of uninitialized value in concatenation (.) or string at
> /usr/local/rrdtool-1.2.23/lib/perl/5.8.5/RRDp.pm line 170.
> BUFFER:
> Use of uninitialized value in concatenation (.) or string at ./test.pl
> line 9.
>
> Closer inspection of the 'read' code suggests that if times are returned
> in the OK string from the call to rrdtool, their values are returned in
> the sys, user and real variables and that $buffer, which is 'undef' at
> this point is returned as the value of the function which is exactly
> what I'm seeing.  It's only when the return from rrdtool doesn't return
> ERROR and it also doesn't return OK with properly formatted time strings
> that $buffer is actually set  to a real value.  So if that's the case,
> how is one to tell if the function succeeded or failed  when you get a
> valid OK with times since it returns 'undef' in both cases?
>
> Next I tried causing an error by trying to rewrite the same data and
> again looking at the code can see when RRDp::read generates an error it
> croaks, but I also found I could set RRDp::error_mode to 'catch' and it
> will simply return the error in the RRDp::error variable.  Only problem
> is it never returns to me!  I put a print statement in the 'read'
> function before the croak test and another in my calling program right
> after the call to 'read' and what I see is:
>
> [root at poker rrd]# ./test.pl
> Error!  Mode: catch   <<<< my print did this and verified it indeed saw
> my value of 'croak'
>
> and it hangs.  Has anyone seen this behavior before?  I'm running
> RHEL4/Update4 on an AMD box.
>
> -mark
>
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