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20050510: LDM data feed question

Celia,

Are you doing any pqact processing on this new machine?
We found previously that your pqact.conf processing on rasp.rap.ucar.edu
was filing every single 100 radial chunk to a separate file, and that 
machine was IO bound and unable to keep up. We made some suggestions, but you
did say you backed out of some of them due to your user need- so that
problem we identified may still exist on your end.

If you turned on the feed on your new machine and are processing similar
pqact.conf actions, you are going down the same path. I suggest that you 
comment out
your pqact entry in ldmd.conf for your relay test if it is critical that you
relay from this machine for a demo at this moment.

If the new machine is not doing any processing and still falls behind in 
relaying data, that would be strange.

Steve Chiswell
Unidata User SUpport



>From: Celia Chen <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200505102049.j4AKnoP3014554

>Dear Support,
>
>I think I just found something interesting in LDM data feed and hope you can h
> elp me
>explain this. 
>
>I have been getting NEXRAD2 data feed from thelma to 3 of my 4 ldm hosts. I ha
> ve been
>having problems with two of the feeds some times in the last couple months.  J
> ust 
>like the situations described below, one feed would be on time but the others 
> would
>have latency problems during some period of time. 
>
>Today I decided to experiment with my 4th ldm host to see if it gets the
>NEXRAD2 data feed directly from thelma. Because I may need to use that machine
>  as the
>primary LDM relay machine in the near future. I turned on the feed before lunc
> h and
>it started to receive level-2 data.  However, a user was in my office when I c
> ame back
>from lunch. There is a 30 minutes latency on the level-2 data feed to her down
> stream
>ldm host and she has a realtime demo in about 30 minutes. What is wrong with t
> he feed?
>
>I right-a-way turned off the level-2 data feed on my 4th ldm host and watched 
> the feed 
>getting back on time in the next few minutes in front of our eyes. 
>
>
>My question is: why the latency problem showed up after I turned on the 4th fe
> ed. Is this
>a local network problem or something else?
>
>Thanks in advance.
>
>Celia
>
>
>
>On Thu, May 05, 2005 at 06:06:33PM -0600, Celia Chen wrote:
>> Dear Support,
>> 
>> I have a question on the time stamps that we see when we do ldmadmin watch:
>> 
>> May 05 23:07:18 pqutil:    23416 20050505220555.112 NEXRAD2 172007  L2-BZIP2
> /KGJX/20050505220505/172/7
>> May 05 23:07:18 pqutil:     6001 20050505220555.561 NEXRAD2 986005  L2-BZIP2
> /KDDC/20050505220444/986/5
>> May 05 23:07:18 pqutil:    13022 20050505220555.212 NEXRAD2 66012  L2-BZIP2/
> KAMX/20050505220506/66/12
>> May 05 23:07:18 pqutil:    29997 20050505220555.128 NEXRAD2 916024  L2-BZIP2
> /KGLD/20050505220419/916/24
>> 
>> I assume that the time on the left is the data arrival time, the time in the
>  middle is when the file
>> was sent by the upstream host, and the time on the right is the time when th
> e file was
>> generated.
>> 
>> Both our LDM hosts rasp and level are getting NEXRAD2 data from thelma.  The
> y both request the
>> NEXRAD2 data directly from thelma.  For some reason, there was a huge
>> (~ 1 hour) latency on rasp this afternoon, as you can see from the above lis
> t. But somehow
>> the same feed on level was very much on time.  Unfortunately I don't have th
> e watch on for the
>> same time period on level. 
>> 
>> Is my assumption correct about the time stamps? If so, why do we see the big
>  difference on the
>> time stamps (from thelma) between rasp and level, therefore the data latency
>  on rasp but not 
>> on level?
>> 
>> Thanks in advance.
>> 
>> Celia.
>
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