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19990615: ldm pq

>From: Jim Cowie <address@hidden>
>Organization: .
>Keywords: 199906151511.JAA21219

>
>This has come up before and I wonder if there is a solution.
>There are times when I want to make an existing LDM product queue a
>little bit larger. The only way I know to deal with this is to 
>re-create the queue at the larger size (ldmadmin mkqueue -c) but
>this destroys the existing queue and all data in it. So upon restarting
>the ldm, you get all the last hours data _again_ from the upstream
>source
>which I don't want. An alternative is to edit the ldmadmin and set
>the rpc.ldmd -o option to 0 to prevent it from getting those old
>products. But that's cumbersome, since normally I want to leave
>that alone inside the ldmadmin script. Is there any way of resizing
>the existing queue (without destroying data) or copying the old queue
>contents to the new queue?
>
>Thanks in advance,
>
>-jim
>
>-----------------------------------------------------------------
>Jim Cowie                              Software Engineer
>WITI Corporation                       address@hidden
>Boulder, CO                            (303) 497-8584
>


Jim,

The LDM product queue can grow as needed, however, the configure script
defines NO_GROW for several platforms including solaris. On Irix, which 
I run the Conduit data feed on, the default is to allow the queue to grow.
The downside of having a growable queue is that there is no high water mark-
and its possible that when pqexpire is running and the queue is growing, 
the lock on the queue can really get slow. In general, I create the queue as 
large
as I expect to need- so the queue won't have to grow often- but if a need
should arise, then it is possible. I wouldn't suggest creating a default 35mb
queue and have the data push it up to its normal running level though
sinceyou will almost definitely run into conflict with pqexpire if
you are growing that much. Anyhow, you can grow the queue but its a compile
time option. If you mainly need to resize the queue on a quiescent system
it should be OK.


Steve Chiswell