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20050812: radar lag?
- Subject: 20050812: radar lag?
- Date: Fri, 12 Aug 2005 09:00:30 -0600
>From: Brendon Hoch <address@hidden>
>Organization: Plymouth State University
>Keywords: 200508121359.j7CDxFjo001287 IDD FNEXRAD latency pqact kill -USR2
Hi Brendon,
>We're seeing some latency in some of our national nexrad radar data,
>files coming in are about an hour old:
>
>%pwd
>/huge/sdata/nowrad/1KN0R-NAT
>%ls -lt | more
>total 60176512
>-rw-r--r-- 1 ldm usr 14208533 Aug 12 13:29 BREF_20050812_1229
>-rw-r--r-- 1 ldm usr 14208533 Aug 12 13:24 BREF_20050812_1224
>-rw-r--r-- 1 ldm usr 14208533 Aug 12 13:19 BREF_20050812_1220
>-rw-r--r-- 1 ldm usr 14208533 Aug 12 13:14 BREF_20050812_1216
>-rw-r--r-- 1 ldm usr 14208533 Aug 12 13:09 BREF_20050812_1211
>
>Looks like the lag started around 5Z and increased from there. Any
>feedback is appreciated.
I just checked the data on atm.geo.nsf.gov (your IDD upstream feed host)
and see that the national 1km N0R (BREF) product is current:
IMGLIST NEXRCOMP/1KN0R-NAT.ALL
Image file directory listing for:NEXRCOMP/1KN0R-NAT
Pos Satellite/ Date Time Center Band(s)
sensor Lat Lon
--- ------------- ------------ -------- ---- ---- ------------
1 RADAR 12 AUG 05224 07:14:00 TWX 27
...
90 RADAR 12 AUG 05224 14:17:00 TWX 27
91 RADAR 12 AUG 05224 14:21:00 TWX 27
92 RADAR 12 AUG 05224 14:26:00 TWX 27
93 RADAR 12 AUG 05224 14:31:00 TWX 27
IMGLIST: done
I ran the McIDAS IMGLIST command at 14:41Z; the most recent image is 14:31,
so the data is getting to atm on time.
The next thing I did was look at the data reception at Plymouth (on pscwx):
http://my.unidata.ucar.edu/content/software/idd/rtstats/siteindex.php?pscwx.plymouth.edu
Latency for FNEXRAD products:
http://my.unidata.ucar.edu/cgi-bin/rtstats/iddstats_nc?FNEXRAD+pscwx.plymouth.edu
Histogram for latency for FNEXRAD products:
http://my.unidata.ucar.edu/cgi-bin/rtstats/iddbinstats_nc?FNEXRAD+pscwx.plymouth.edu
The histogram plot shows that pscwx is receiving 95% of the FNEXRAD
products within 8 seconds of their being injected into the IDD (and 99%
within 11 seconds).
Given that the products are being delivered to pscwx within a few
seconds of their IDD insertion time, and given that the products on
your upstream feed host are current, my conclusion is that the
processing of the data out of the LDM queue on pscwx must be slow. If
you have lots of pqact.conf actions for a single invocation of pqact,
then this would explain it taking longer and longer to process the
products out of the queue. So, I would check your LDM to see if it is
struggling to process products already received:
<as 'ldm'>
kill -USR2 <pid of pqact>
kill -USR2 <pid of pqact>
The two kills will put pqact into a debug logging state. One of the
things that will be listed will be how long it is taking to process
data out of the queue. What you want to look for are Delay and
pq_sequence messages since they will tell you the 'time elapsed' when
processing a product.
NOTE: don't leave your system in debug logging mode for long -- the
log output is _significant.
>Thanks,
No worries.
Cheers,
Tom
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