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[LDM #QAV-891001]: Receiving duplicate GRIB messages over LDM

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  • Subject: [LDM #QAV-891001]: Receiving duplicate GRIB messages over LDM
  • Date: Fri, 11 May 2007 14:17:07 -0600
Hi Kevin,

re:
> I have been having problems with receiving some GRIB messages multiple
> times (usually twice) over the LDM.
> 
> This is on the machine stimpy.ssec.wisc.edu.
> One example is today's (May 11) 12 Z GFS global forecast.
> First, I get a 500 MB Temperature come in at 15:29:01 Z
> Then, I get the same 500 MB Temperature come again at 16:12:21 Z.
> I have a 4 G queue size on stimpy and am receiving HRS, CONDUIT, and
> NGRID data (GRIB-1 and GRIB-2) data to this machine.

The first question is:

- what is the age of the oldest product in your LDM queue?  You can determine
  this using the LDM 'pqmon' utility:

<as 'ldm'>
pqmon -l-

You should run this as soon as possible after the receipt of a duplicate 
product.
If the age of the oldest product in the queue (listed in seconds) is less than
the time difference between receipt time of the duplicate and the original, it 
means
that the LDM has no way of determining that the product is a duplicate since
the original is no longer in the queue.

The second possibility is that the same GRIB message is contained in more than
one datastream and its MD5 signature is different so it is not seen as being
the same product by the LDM's duplicate product detection and rejection 
facility.
You can use the LDM 'notifyme' utility to list out information on products 
received,
and this will include the name of the datastream the product was in.  It will
greatly help if you can specify a regular expression pattern to use for which
product(s) to list, otherwise there will be lots of entries in the list of
products and you will have to sift through them to find the information you
are looking for.

> Thanks for any insight!

Please try the suggestions above and let us know what you find.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: QAV-891001
Department: Support LDM
Priority: Normal
Status: Closed