[Oisf-users] Question Regarding Prune Statistics

Rasmor, Zachary R zachary.r.rasmor at lmco.com
Thu Apr 9 19:19:53 UTC 2015



I am trying to make sense of the positive "pruned" values that I'm seeing in
my stats log. My understanding is that positive prune values are
undesirable; however my understanding was also that pruning occurs in
emergency mode after shortened timeouts have not stabilized memory usage.


l :


"At the point the memcap will still be reached, despite prealloc, the
flow-engine goes into the emergency-mode. In this mode, the engine will make
use of shorter time-outs. It lets flows expire in a more aggressive manner
so there will be more space for new Flows. 
There are two options: emergency_recovery and prune_flows. The emergency
recovery is set on 30. This is the percentage of prealloc'd flows after
which the flow-engine will be back to normal (when 30 percent of the 10000
flows is completed).
If during the emergency-mode, the aggressive time-outs do not have the
desired result, this option is the final resort. It ends some flows even if
they have not reached their time-outs yet. The prune-flows option shows how
many flows there will be terminated at each time a new flow is set up."


I have pasted the final stats entry of a 30 min test below. As you can see,
I never entered emergency mode, however my positive prune statistics.

(One additional note about the passage above: the "prune-flows" setting
seems to have been deprecated as of v1.3.1) 


flow_mgr.closed_pruned    | FlowManagerThread         | 5016163

flow_mgr.new_pruned       | FlowManagerThread         | 1121133

flow_mgr.est_pruned       | FlowManagerThread         | 1885848

flow.memuse               | FlowManagerThread         | 1433762256

flow.spare                | FlowManagerThread         | 2097144

flow.emerg_mode_entered   | FlowManagerThread         | 0

flow.emerg_mode_over      | FlowManagerThread         | 0


This leads to a few questions:


1.       Are positive pruned values necessarily a bad thing? 

2.       Per the Suricata training class: "new_pruned means flow were
discarded before they were established" - what is the meaning of est_pruned
and closed_pruned?

3.       How is pruning occurring if we never enter emergency mode?





Zach Rasmor

Senior Software Engineer

Lockheed Martin CIRT

700 N Frederick Ave | Gaithersburg, MD 20879

Email: zachary.r.rasmor at lmco.com

Office: 301.240.6116

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