[rrd-users] Re: fetching only non-NAN values / non verbose / extrapolating

Alex van den Bogaerdt alex at ergens.op.HET.NET
Sun Aug 11 00:09:03 MEST 2002

Cheng Hu wrote:

> Problem 4
> =========
> I was wondering if there is a way to specify to fetch to print out only
> those records that contain some non-NAN value.

No, not that I know of.  Of course you can filter, using grep.

> Problem 5
> =========
> I was wondering if there is a way to turn off what rrdtool writes to
> stdout while in remote control mode.

Again: filter.

> Problem 6
> =========
> I am using the following create command:
> 	  fprintf(rrdtool_stdin,
> 		  "create tcp_test_data_%lu.rrd" \
> 		  " --start %d" \
> 		  " --step 1000" \
> 		  " DS:congestion_window:GAUGE:%lu:0:U" \
> 		  " DS:receive_ack:GAUGE:%lu:0:U" \
> 		  " RRA:MAX:0.99:1:%u" \
> 		  " RRA:AVERAGE:0.99:1:%u" \
> 		  "\n",
> 		  cd->id, UTC_1980, ULONG_MAX, ULONG_MAX,
> 		  TEST_DURATION * 1000, TEST_DURATION * 1000);
> I was wondering since heartbeat is here set to ULONG_MAX (maximum possible
> value for unsigned long), shouldn't RRDTool attempt to extrapolate all NAN
> points when it fits the input data into Primary Data Points?

I think it should.  Are you sure you understand when RRDtool generates the
PDPs ?  If you are, try a number slightly lower than half of ULONG_MAX
and see if that works.  If it does, there's a sign bug somewhere (could
be in your program or in RRDtool).

Thinking of signs, you are telling RRDtool to write NaN into the database
when it receives a negative number ...

> This is what I'd like it to do. When it fits actual inputed data to PDPs,
> if for a particular step it is missing data, I'd like it to extrapolate
> the point by simply making the value equal the last non-NAN value. Is

Uh, no.  When you update the database, the rate calculated is valid from
the previous update upto the current one.  NaN is also a rate (not really,
but for this explanation it is).  Fact is, NaN should not occur unless you
expect it to happen.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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