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[LDM #AET-785898]: primary/alternate

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  • Subject: [LDM #AET-785898]: primary/alternate
  • Date: Wed, 14 Jun 2006 09:15:11 -0600
Hi Karen (long time no hear :-)

> Sorry if this has been asked before, I searched the archives and
> couldn't find anything.  We are using LDM-6.4.1 to ship some of our
> products around between machines (using EXP feedtype).    The data all
> seems to be getting through, but the connections keep "flipping" between
> primary and alternate modes.   I know the primary mode is more
> efficient, but I'm not sure why it is flipping back and forth.

Every minute, a downstream LDM re-evaluates its reception mode (PRIMARY or
ALTERNATE) and switches if it should, depending on the rate of successful 
insertions
into the product-queue.  If it's in PRIMARY mode, then it will switch to 
ALTERNATE mode if it's not responsible for most of the insertions and vice
versa.

> Does this indicate a delay in the data?

More than anything else, it indicates that the multiple upstream LDM-s
from which you're getting data are at electronically similar distances
from the receiving LDM.

> And, is there any way to force the
> connections to always be primary mode?

No, and I don't think you'd want that.  It does tend to pollute the log
file, however, which is why I usually use grep(1) when perusing the log
file.

Now, having said all that, I note the following in the CHANGE_LOG file
for a more recent version of the LDM than the one you're using:

        Corrected checking of saved product-information by a downstream
        LDM if the number of hosts sending the same products is two or
        more.  This should decrease the rate of transfer-mode switching.

You might try the latest version of the LDM to see if the switching-rate
is less.  I recommend the beta version

    ftp://ftp.unidata.ucar.edu/pub/ldm/beta/ldm-6.4.6.4.tar.Z

> Beware programmers who carry screwdrivers.

Hey!  I got a screwdriver -- and I'm not afraid to use it!  :-)

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: AET-785898
Department: Support LDM
Priority: Normal
Status: Closed