20031125: ldm/craft data latencies at NWS Central Region HQ

Karen,

The cause of the large latencies from the LDM at the KBIS WFO was due
to the SIGCONT signals from the radar ingester not being delivered to
the LDM because the radar ingester was not in the process-group of the
LDM (SIGCONT is used to signal that a data-product has just been added
to the product-queue).  This caused the LDM to fallback to polling the
product-queue every 30 seconds -- resulting in the large latencies.
Based on the latency records in the file

    
/home/ldm/data/rtstats/CRAFT/20031126/ldmradar2.crh.noaa.gov/kbis.bis.noaa.gov_v_204.227.116.90

the latency statistics of this setup are the following:

    number of latency records:  1009
    minimum latency:               0 s
    maximum latency:              30 s
    mean latency:                 18.3657 s
    latency standard deviation:    7.1399 s

The solution was to move the execution of the radar ingester from
outside the LDM process-group to inside the LDM process-group by having
it executed via an EXEC entry in the KBIS LDM configuration-file
(ldmd.conf).

Here's what I did:

    * Changed /etc/init.d/ldm (the original file is "ldm.orig"):

        * Removed the execution of the radar ingester (pqing_bdds).

        * Followed the example at

            
http://my.unidata.ucar.edu/content/software/ldm/ldm-6.0.14/basics/configuring.html#boot

          for the "start" action.

    * Changed the LDM configuration-file (/home/ldm/etc/ldmd.conf) by
       adding an EXEC entry for the radar ingester (pqing_bdds).

    * Stopped the radar ingester by sending it a SIGTERM.

    * Restarted the LDM via an "ldmadmin stop" and "ldmadmin stat".

As of 2003-11-26 17:10:54 UTC, the KBIS LDM is using this new
configuration.

Based on the latency records in the previously-mentioned file,
the above chages have resulted in the following latency statistics:

    number of latency records:  48
    minimum latency:             0 s
    maximum latency:             1 s
    mean latency:                0.275862 s
    latency standard deviation:  0.450851 s

We strongly recommend that the configuration of all WFO LDM-s be changed
to match this new configuration of the LDM at KBIS.

Regards,
Steve Emmerson
Tom Yoksas