Marc Lehmann > AnyEvent-SNMP-6.0 > AnyEvent::SNMP

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Module Version: 6.0   Source  

NAME ^

AnyEvent::SNMP - adaptor to integrate Net::SNMP into AnyEvent.

SYNOPSIS ^

 use AnyEvent::SNMP;
 use Net::SNMP;

 # just use Net::SNMP and AnyEvent as you like:

 # use a condvar to transfer results, this is
 # just an example, you can use a naked callback as well.
 my $cv = AnyEvent->condvar;

 # ... start non-blocking snmp request(s)...
 Net::SNMP->session (-hostname => "127.0.0.1",
                     -community => "public",
                     -nonblocking => 1)
          ->get_request (-callback => sub { $cv->send (@_) });

 # ... do something else until the result is required
 my @result = $cv->wait;

DESCRIPTION ^

This module implements an alternative "event dispatcher" for Net::SNMP, using AnyEvent as a backend. This integrates Net::SNMP into AnyEvent. That means you can make non-blocking Net::SNMP calls and as long as other parts of your program also use AnyEvent (or some event loop supported by AnyEvent), they will run in parallel.

Also, the Net::SNMP scheduler is very inefficient with respect to both CPU and memory usage. Most AnyEvent backends (including the pure-perl backend) fare much better than the Net::SNMP dispatcher.

Another major added fetaure of this module over Net::SNMP is automatic rate-adjustments: Net::SNMP is so slow that firing a few thousand requests can cause many timeouts simply because Net::SNMP cannot process the replies in time. This module automatically adapts the send rate to avoid false timeouts caused by slow reply processing.

A potential disadvantage of this module is that replacing the dispatcher is not at all a documented thing to do, so future changes in Net::SNP might break this module (or the many similar ones).

This module does not export anything and does not require you to do anything special apart from loading it before doing any non-blocking requests with Net::SNMP. It is recommended but not required to load this module before Net::SNMP.

GLOBAL VARIABLES ^

$AnyEvent::SNMP::MAX_OUTSTANDING (default: 50, dynamic)
AnyEvent::SNMP::set_max_outstanding $new_value

Use this package variable to restrict the number of outstanding SNMP requests at any point in time.

Net::SNMP is very fast at creating and sending SNMP requests, but much slower at parsing (big, bulk) responses. This makes it easy to request a lot of data that can take many seconds to parse.

In the best case, this can lead to unnecessary delays (and even time-outs, as the data has been received but not yet processed) and in the worst case, this can lead to packet loss, when the receive queue overflows and the kernel can no longer accept new packets.

To avoid this, you can (and should) limit the number of outstanding requests to a number low enough so that parsing time doesn't introduce noticable delays.

Unfortunately, this number depends not only on processing speed and load of the machine running Net::SNMP, but also on the network latency and the speed of your SNMP agents.

AnyEvent::SNMP tries to dynamically adjust this number upwards and downwards.

Increasing $MAX_OUTSTANDING will not automatically use the extra request slots. To increase $MAX_OUTSTANDING and make AnyEvent::SNMP make use of the extra paralellity, call AnyEvent::SNMP::set_max_outstanding with the new value, e.g.:

   AnyEvent::SNMP::set_max_outstanding 500;

Although due to the dynamic adjustment, this might have little lasting effect.

Note that you can use Net::SNMP::XS to speed up parsing of responses considerably.

$AnyEvent::SNMP::MIN_RECVQUEUE (default: 8)
$AnyEvent::SNMP::MAX_RECVQUEUE (default: 64)

These values specify the minimum and maximum receive queue length (in units of one response packet).

When AnyEvent::SNMP handles $MAX_RECVQUEUE or more packets per iteration it will reduce $MAX_OUTSTANDING. If it handles less than $MIN_RECVQUEUE, it increases $MAX_OUTSTANDING.

This has the result of adjusting the number of outstanding requests so that the recv queue is between the minimum and maximu, usually.

This algorithm works reasonably well as long as the responses, response latencies and processing times are the same size per packet on average.

COMPATIBILITY ^

This module may be used as a drop in replacement for the Net::SNMP::Dispatcher in existing programs. You can still call snmp_dispatcher to start the event-loop, but then you loose the benefit of mixing Net::SNMP events with other events.

   use AnyEvent::SNMP;
   use Net::SNMP;

   # just use Net::SNMP as before

   # ... start non-blocking snmp request(s)...
   Net::SNMP->session (
         -hostname    => "127.0.0.1",
         -community   => "public",
         -nonblocking => 1,
      )->get_request (-callback => sub { ... });

   snmp_dispatcher;

SEE ALSO ^

AnyEvent, Net::SNMP, Net::SNMP::XS, Net::SNMP::EV.

AUTHOR ^

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/
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