[Query Cache] Add a dynamic cluster setting to change skip cache factor

[sgup432]

Is your feature request related to a problem? Please describe

Recently, a change was added in lucene LRU cache where we can dynamically change skip cache factor to increase the cache utilization. Someone had posted performance benefits here by relaxing skip cache factor limits and utilizing cache more.

We can add a cluster setting at our end to achieve this. Also explore in what cases(to what values) we can use this to achieve benefits.

Describe the solution you'd like

Add a dynamic cluster setting

Related component

No response

Describe alternatives you've considered

No response

Additional context

No response

[sandeshkr419]

[Search Triage] That will be great, lets see if someone from community is interested in working on this.

[kkewwei]

[Search Triage] That will be great, lets see if someone from community is interested in working on this.

I'd great to support this feature when the new lucene is released, If @sgup432 agrees.

[sgup432]

Also, in addition to this, we need to expose a dynamic setting to update the frequency based caching policy for QueryCache.
As of now, it only caches query when it has seen the same query for 5 times, see here.

Exposing this setting will give us an opportunity to update the value to a lower number, thereby increasing cache utilization if needed.

[kkewwei]

@sgup432 I attempted to make the frequency value dynamic but failed. While I can override the minFrequencyToCache method, I'm unable to reuse the isCostly method since it's not declared as public.

If we want to make the frequency value dynamic, there seems one way to implement:

• Disregard the "costly" classification.

           cachingPolicy = new UsageTrackingQueryCachingPolicy() {
                @Override
                protected int minFrequencyToCache(Query query) {
                    int minFrequency = this.minFrequency;
                    if (query instanceof BooleanQuery || query instanceof DisjunctionMaxQuery) {
                        --minFrequency;
                    }

                    return Math.max(0, minFrequency);
                }
            };

I'm uncertain whether this is the optimal implementation path or if maintaining the frequency status quo is preferable.