[mod_cluster-issues] [JBoss JIRA] (MODCLUSTER-393) One can't change history and decay with DynamicLoadBalanceFactorProvider

[Michal Babacek (JIRA)]

    [ https://issues.jboss.org/browse/MODCLUSTER-393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12952263#comment-12952263 ] 

Michal Babacek commented on MODCLUSTER-393:
-------------------------------------------

(Actually [~pferraro] is the author of the class in question, so I might have picked a wrong assignee...)
                
> One can't change history and decay with DynamicLoadBalanceFactorProvider
> ------------------------------------------------------------------------
>
>                 Key: MODCLUSTER-393
>                 URL: https://issues.jboss.org/browse/MODCLUSTER-393
>             Project: mod_cluster
>          Issue Type: Bug
>    Affects Versions: 1.2.6.Final
>            Reporter: Michal Babacek
>            Assignee: Radoslav Husar
>            Priority: Critical
>         Attachments: redacted_log
>
>
> I'm under an ugly impression that one can't actually change {{history}} and {{decay}} attributes of *DynamicLoadBalanceFactorProvider*.
> I was trying to figure out why the new test suite of CustomLoadMetric tests does not pass. In order to get load figures without history and decay manipulation, I set the following:
> {code}
> <subsystem xmlns="urn:jboss:domain:modcluster:1.2">
>     <mod-cluster-config advertise-socket="modcluster" connector="ajp">
>     <dynamic-load-provider history="0">
>         <custom-load-metric class="biz.karms.modcluster.CustomLoadMetric" weight="1">
>             <property name="capacity" value="1000"/>
>             <property name="loadfile" value="/tmp/mod_cluster-eapx/loadfileA"/>
>             <property name="parseexpression" value="^LOAD: ([0-9]*)$"/>
>         </custom-load-metric>
>     </dynamic-load-provider>
>     </mod-cluster-config>
> </subsystem>
> {code}
> The aforementioned {{history=0}} effectively means that there is just 1 "slot" for a one historical value on which decay function should work.
> If you take a look at the code in [DynamicLoadBalanceFactorProvider|https://github.com/modcluster/mod_cluster/blob/master/core/src/main/java/org/jboss/modcluster/load/impl/DynamicLoadBalanceFactorProvider.java#L54] constructor, it is apparent
> that the size of the List that later serves for storing the historical values is set sooner than the actual [setHistory(int history)|https://github.com/modcluster/mod_cluster/blob/master/core/src/main/java/org/jboss/modcluster/load/impl/DynamicLoadBalanceFactorProvider.java#L177] method is called.
> The actual size of that List collection wouldn't do any harm by itself but it is being used in the aforementioned class with {{.size()}} to control cycles.
> The same IMHO holds for the decay attribute.
> Anyhow, I put some additional logging to the [DynamicLoadBalanceFactorProvider.java|https://github.com/modcluster/mod_cluster/blob/master/core/src/main/java/org/jboss/modcluster/load/impl/DynamicLoadBalanceFactorProvider.java]:
> {code}
> // Historical value contribute an exponentially decayed factor
> for (int i = 0; i < queue.size(); ++i) {
>     double decay = 1 / Math.pow(decayFactor, i);
>     totalDecay += decay;
>     this.log.info("KTAG: totalLoad:"+totalLoad+", with decay:"+(totalLoad+queue.get(i).doubleValue() * decay));
>     totalLoad += queue.get(i).doubleValue() * decay;
> }
> {code}
> and
> {code}
> try {
>     // Normalize load with respect to capacity
>     this.recordLoad(metricLoadHistory, metric.getLoad(engine) / metric.getCapacity());
>     this.log.info("KTAG metricLoadHistory:"+metricLoadHistory.toString());
>     totalWeight += weight;
>     totalWeightedLoad += this.average(metricLoadHistory) * weight;
> } catch (Exception e) {
>     this.log.error(e.getLocalizedMessage(), e);
> }
> {code}
> with the following being the output: [^redacted_log].
> So, despite having {{history=0}}, which should force the system to keep just 1, the current value, {{metricLoadHistory}} grew from
> {noformat}
> KTAG metricLoadHistory:[0.8]
> {noformat}
> to
> {noformat}
> KTAG metricLoadHistory:[0.9, 0.9, 0.9, 0.9, 0.9, 0.9, 0.9, 0.9, 0.9, 0.8]
> {noformat}
> which is exactly [9|https://github.com/modcluster/mod_cluster/blob/master/core/src/main/java/org/jboss/modcluster/load/impl/DynamicLoadBalanceFactorProvider.java#L50] + [1|https://github.com/modcluster/mod_cluster/blob/master/core/src/main/java/org/jboss/modcluster/load/impl/DynamicLoadBalanceFactorProvider.java#L54] in size :-)
> WDYT?

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