I have a sub-agent which provides access to a table that is fairly expensive to build
and I'm hoping someone who's done this before has an idiom that'll help me lighten the
load on my system and respond more quickly to requests.
I've used mib2c 5.1.1 to generate code for dot1dTpPortFdbTable (.1.3.6.1.2.1.17.4.3)
then filled in the generated functions. As I understand it -- and I'm happy to be
corrected -- when a request comes in for table data, the (sub-)agent gathers
information about the size of the table and its keys (with
dot1dTpFdbTable_get_first_data_point() and dot1dTpFdbTable_get_next_data_point()) then
uses that information to figure out what keys to give get_dot1dTpFdbAddress(), etc. to
get all the data necessary to satisfy all the requests in the message. Right so far?
My first-pass implementation gets external data and caches it in an array of
structures inside the get_*_data_point() routines but it takes a while. As a result,
if a client asks for individual values from the table (one request per message), then
I build the table over and over again, incurring all of the overhead on every request.
One solution would be to put some sort of timer on my cache so that I don't refill it
for _every_ message. That has problems with stale data, etc.
It's fairly easy and cheap for me to get _one_ record for one MAC address
(dot1dTpFdbAddress), if there were just some way to bypass the get_*_data_point()
routines and let the data access routine build individual records in the cache (or
return data directly) but I don't see how the table iterator architecture lets me do
that.
I could also do some fancy coding to spread the load of building the cache over
multiple calls but that also give me stale data (not to mention complex code that's
harder to maintain).
I'd rather not have to recode without the table helpers but I seem to have a mismatch
between my requirements and the table interator stuff. I hope someone more familiar
with this area can provide some net-snmp insight.
TIA.
Chris
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