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Which Eviction Policy threshold triggers aggressive connection reaping?

rob_carr
MVP
MVP

I'm getting mixed messages about what triggers connection reaping behavior on the BIG-IP. Is it utilization passing the high-water mark or the low-water mark? K15821 says that the trigger is passing the high-water mark, K15740 says that the trigger is passing the low-water mark (F5 training materials also say the trigger is passing the low-water mark).

 

From K15821: Overview of eviction policies:

 

Trigger

The High Water and Low Water thresholds configured in an eviction policy trigger when the adaptive connection reaping behavior starts and stops.

  • High Water: Specifies the percentage of the quota for this context before flow eviction starts (defaults to 95 percent).
  • Low Water: Specifies the percentage of the quota for this context before flow eviction ends, and processing of new flows resumes, after the high water mark is reached (defaults to 85 percent).

 

From K15740: Overview of adaptive connection reaping (11.6.0 and later):

Within an eviction policy, the high-water and low-water thresholds specify the resource quota percentage used to trigger when the adaptive connection reaping behavior starts and stops.

  • High-water: Specifies the target maximum load on the context. The adaptive reaper becomes more aggressive as this limit is approached. The allowable range is 50 to 100, and the high-water value must be higher than or equal to the low-water value.
  • Low-water: Specifies the aggressive sweeper activation threshold as a percentage of total capacity. The allowable range is 50 to 100, and the low-water value must be lower than or equal to the high-water value.

 

K156740 has been updated more recently than K15821, so it's possible that there has been a change in behavior between v13 and v14, and this is reflected in the dissonance between K15821 and K156740 (not that the 14.0 of 14.1 release notes say anything).

3 REPLIES 3

Nathan_F__F5_
F5 Employee
F5 Employee

Hi Rob,

 

What section of article K15821 says that the adaptive reaping isn't triggered until the high water mark is reached? Maybe I am just missing that part but I don't see where it explicitly says that. Either way, please let me know because I would like to have that changed if it does say that somewhere.

 

Regarding your question, the low-water mark is where the sweeper triggers initially. It then becomes more aggressive as it gets closer to the high-water mark. There is a third article that explains this a bit more.

 

K15738: Low Water and High Water values for adaptive connection reaping are now configured in an eviction policy

https://support.f5.com/csp/article/K15738

 

Please see the "New Behavior" section in the article. Hopefully this answers you question.

 

-Nathan F

Hi Nathan,

 

In Solution K15821, under the 'Trigger' heading, the High Water value is defined as "Specifies the percentage of the quota for this context before flow eviction starts (defaults to 95 percent)." (Emphasis added)

 

Under the same heading, the Low Water value is defined as "Specifies the percentage of the quota for this context before flow eviction ends, and processing of new flows resumes, after the high water mark is reached (defaults to 85 percent)." (Emphasis added)

 

Solution K15738 was a good reference to point out, as it makes it plain that the information in K15821 was written in terms of the pre-11.6.0 behavior - "Once memory utilization reaches the high-water mark, the system does not allow new connections until the available memory is reduced to the low-water mark threshold." (Emphasis added)

 

Thanks for taking a look at this.

 

-Rob C

 

 

 

I definitely see what you mean now. That is definitely a bit contradictory. I'll look into having the article corrected and updated with better working if possible. Thank you for the clarification!