Many Thanks,
Francois
2012/2/15 Dave Shield <d.t.shi...@liverpool.ac.uk>
> On 14 February 2012 15:35, Francois Bouchard <francois.bouch...@mpbc.ca>
> wrote:
> > Here is the code for a cached snmp table module.
>
> OK - I've tried compiling and running that module.
>
> The timeout specified in the header file is given as
> #define MPBCRMHALARMTABLE_TIMEOUT 10
> and that's exactly what I'm seeing.
>
> The agent generates a log message whenever the load routine
> is called, so if I run this in one window, I'd expect see a series
> of messages of the form
> mpbcRMHAlarmTable_load: loaded ....
> mpbcRMHAlarmTable_free
> mpbcRMHAlarmTable_load: loaded ....
> mpbcRMHAlarmTable_free
> whenever the table is loaded or freed.
>
>
> If I run a series of GETNEXT requests on this table in a different
> window, with a few seconds between them, then I see the following
> behaviour:
>
> snmpgetnext .... mpbcRMHAlarmTable
> agent prints "loaded" message
> client receives response
> sleep 6
> snmpgetnext .... mpbcRMHAlarmTable
> client receives response - note, nothing printed by the agent
> sleep 6
> snmpgetnext .... mpbcRMHAlarmTable
> agent prints "free" message
> agent prints "loaded" message
> client receives response
> sleep 60
> agent prints "free" message
>
>
>
> Note that when the agent receives a request for something in this
> table and the cache is older than the defined timeout (12s > 10s),
> then it *does* re-load the data. This is the expected behaviour.
>
> However the agent does not automatically release the local cache
> (i.e. call the 'free' routine) as soon as the timeout has expired.
> Instead this is handled by a regular "garbage collection" run
> (once a minute), which will free any stale caches.
> In the meantime, a request that tries to use that cache will
> spot that it's expired, and reload the data.
>
> Don't get confused between the granularity of how long the data
> is valid for (and hence when incoming requests will trigger a
> cache reload), and the granularity of garbage collection.
>
> Hope this helps
>
> Dave
>
> PS: Please note that I'll be off-line for the next week or so,
> so if you have any further questions on this, you'll have to
> rely on someone else, or wait for me to get back!
>
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