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[LDM #QKY-452311]: National Weather Service Level II (Information Request)

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  • Subject: [LDM #QKY-452311]: National Weather Service Level II (Information Request)
  • Date: Tue, 22 Jun 2010 17:15:37 -0600
Don & Chris,

> For each radar XXXX:
> 
> request EXP ".XXXX" IP
> 
> The products don't exist...yet. When RPG Build 12 is fielded late Aug to
> late Sept, the EXP product will exist.

I think that's the cause of the slow response.  On the newly-promoted 
aggregation system, each downstream LDM process will search though the 
product-queue for the most-recently received matching data-product.  The LDM 
queue is implemented as a unidirectional skip-list (from oldest data-product to 
most-recent) so searching for the most-recently received data-product is an 
O(log N) operation.  On average, each NEXRAD2-requesting downstream LDM will 
find a matching product after 77 such searches.  Because there are no EXP 
data-products in the queue, however, each EXP-requesting downstream LDM will 
search the entire queue before giving up, which is an O(N log N) operation.  I 
think you have 154 processes searching the entire product-queue for products 
that don't exist and that this is eating-up the CPU-s and delaying the response.

I tested that hypothesis here and the restart time went from 30 seconds at the 
most to about three minutes.  The LDM wasn't relaying any data, so that might 
account for its response being less than 10 minutes.

I suggest that you remove the requests for EXP data until such data-products 
become available.

> Chris
> --
> 
> 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: QKY-452311
Department: Level II
Priority: Normal
Status: Closed