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[LDM #QYR-744357]: increase Q size

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  • Subject: [LDM #QYR-744357]: increase Q size
  • Date: Fri, 27 Jul 2012 16:15:45 -0600
Virginia, Chris, Robert,

> It shows up as "latency" on the NWS website, however, I believe the real
> problem is duplicate data being re-downloaded as the TGP48/49 server (w/
> 2GB queue) switches primary/alternate between the two sources (RDS and TDS
> w/ 4GB queues). LDM seems to start up a new connection when switching
> sources and data that has aged out of the smaller downstream queue is
> re-downloaded from the larger upstream queue. The duplicate data appears as
> a false latency. Please correct me if I'm wrong as most of my LDM knowledge
> if from trial and error....mostly error.

I suspect the large "latencies" you're seeing are due to the size of the 
product-queue being incompatible with the maximum allowed latency parameter, 
which is 1 hour by default. If the product-queue is too small to hold more than 
30 minutes worth of data, then a duplicate data-product that arrives 45 minutes 
late will be accepted as a new data-product because its previous arrival has 
been purged from the product-queue.

Beginning with LDM version 6.9, the LDM system can now automatically reconcile 
the size of the product-queue and the maximum latency parameter, either by 
increasing the size of the queue, decreasing the maximum latency parameter, or 
notifying the LDM user via email -- depending on the value of the 
"reconciliation-mode" parameter. You should be able to find a lot of 
support-email on this subject <http://www.unidata.ucar.edu/software/ldm/#help> 
by searching for "reconciliation-mode". Also, this feature is documented in the 
online LDM reference 
<http://www.unidata.ucar.edu/software/ldm/ldm-6.10.1/basics/index.html>.

> I know there is a flag in LDM to limit the downloading of data to that
> below a certain latency threshold, however, you risk missing data from a
> site that is experiencing actual latency (I've seen individual sites with
> real latency over 3000 seconds due to telco problems).
> 
> --
> Chris Calvert
> Software Engineer
> National Weather Service
> WSR-88D Radar Operations Center
> 1313 Halley Circle, Norman, OK 73069
> (405) 573-3323

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: QYR-744357
Department: Support LDM
Priority: Normal
Status: Closed