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Real-time latencies

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  • Subject: Real-time latencies
  • Date: Thu, 31 Jan 2002 13:20:56 -0700
Jason and Carl,

Here's the info I promised to send you on computing product latencies.

First, it *is* possible to get an accurate (within 1 second) latency
for each product just from the output of either "pqutil -w" or from
running "notifyme -vl-" on the machine that is receiving the products
you want latencies for.  Also, if you have good network connections to
an LDM host and are permitted by an "ALLOW" entry, you can get
accurate latencies for that host.  For example, if I want accurate
product latencies on the MCIDAS feed to motherlode.ucar.edu, I run:

 $ notifyme -vl- -h motherlode.ucar.edu -f MCIDAS
 Jan 31 18:13:56 notifyme[29479]: Starting Up: motherlode.ucar.edu: 
20020131181356.218 TS_ENDT {{MCIDAS,  ".*"}}
 Jan 31 18:13:56 notifyme[29479]: NOTIFYME(motherlode.ucar.edu): OK
 Jan 31 18:15:27 notifyme[29479]:   121702 20020131181510.359  MCIDAS 000  
pnga2area Q0 CA 1100 GOES-10_SND UNKBAND 14km 20020131 1700

 ...

The latency for the product "pnga2area Q0 CA 1100 GOES-10_SND UNKBAND
14km 20020131 1700" is the difference between the time stamp at the
beginning of the line, "Jan 31 18:15:27", and the product injection
time, "20020131181510.359" (which is in the format yyyymmddhhmmss.xxx)
or 17 seconds.  Similarly with the output of "pqutil -w data/ldm.pq",
you can just take the difference of the two times.  And the product
size is also available as the field after the ":", 121702 bytes for
this example product.

Steve Chiswell's real-time latencies package is available from:

  ftp://ftp.unidata.ucar.edu/pub/ldm5/rtstats/rtstats.tar.Z

There will be a README file in the same FTP directory later this
afternoon (if it's not already there) that describes how to install
and use it.  Currently rtstats is being used for creating the real-time
latencies that are plotted at:

  http://www.unidata.ucar.edu/staff/chiz/latency/stats/

for example

  
http://www.unidata.ucar.edu/staff/chiz/latency/stats/NNEXRAD_flood.atmos.uiuc.edu.gif

Let us know if you have more questions about this.

--Russ