Requesting very old data from your upstream host

Hi Karl,

There is no limit as to how far back you can request data from your upstream 
ldm.  The only difficulty is that the arguments to rpc.ldmd are in seconds, so 
you'll have to calculate how many days worth of data you want in terms of 
seconds.  (In the future we may add a suffix flag to the time argument so that 
you could specify times in other units.)

There is a practical limit to how far back in time you can go - the time in 
seconds must fit in 31 bits (assuming the time is a signed value, which I think 
it is, and assuming you're using a 32 bit architecture).  But, that shouldn't 
be a problem for you - 2**30 is 2,147,483,648 seconds, or over 24,000 days.

Use the -m (max latency) flag to rpc.ldmd to do this.  The -o (offset) flag 
refers to what data you want to request upon start up, and the -m flag refers 
to what data you are willing to accept. (You might find yourself accepting 
older data than you would request if your ldm falls behind for some reason.)  
By default, the offset will be the same as the max latency, which is what I 
assume you want, so using the -m flag should work.

You'll probably want to edit the ldmadmin script to implement this change from 
the default set up.  The only downside is that every time you get a new 
distribution you'll have to migrate your changes into the new ldmadmin script 
that came with the distribution.

Good luck, and let me know if you have any further questions.

Anne

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Anne Wilson                     UCAR Unidata Program            
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