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https://issues.apache.org/jira/browse/LUCENE-10068?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17405108#comment-17405108
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Gautam Worah edited comment on LUCENE-10068 at 8/26/21, 9:48 AM:
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Some history here: We previously had a [double barrel
LRU|https://lucene.apache.org/core/3_6_2/api/core/org/apache/lucene/util/DoubleBarrelLRUCache.html]
cache in Lucene 3.6 but we ended up removing it I think. Jira Search throws
some ancient Jira
[tickets|http://jirasearch.mikemccandless.com/search.py?chg=new&text=DoubleBarrelLRUCache&a1=&a2=&page=0&searcher=42159&sort=recentlyUpdated&format=list&id=1xy07b2ketsi&newText=DoubleBarrelLRUCache]
was (Author: gworah):
Some history here: We previously had a[ double barrel
LRU|https://lucene.apache.org/core/3_6_2/api/core/org/apache/lucene/util/DoubleBarrelLRUCache.html]
cache in Lucene 3.6 but we ended up removing it I think. Jira Search throws
some ancient Jira
[tickets|http://jirasearch.mikemccandless.com/search.py?chg=new&text=DoubleBarrelLRUCache&a1=&a2=&page=0&searcher=42159&sort=recentlyUpdated&format=list&id=1xy07b2ketsi&newText=DoubleBarrelLRUCache]
> Switch to a "double barrel" HPPC cache for the taxonomy LRU cache
> -----------------------------------------------------------------
>
> Key: LUCENE-10068
> URL: https://issues.apache.org/jira/browse/LUCENE-10068
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/facet
> Affects Versions: 8.8.1
> Reporter: Gautam Worah
> Priority: Minor
>
> While working on an unrelated getBulkPath API
> [PR|https://github.com/apache/lucene/pull/179], [~mikemccand] and I came
> across a nice optimization that could be made to the taxonomy cache.
> The taxonomy cache today caches frequently used ordinals and their
> corresponding FacetLabels. It uses the existing LRUHashMap (backed by a
> LinkedList) class for its implementation.
> This implementation performs sub optimally when it has a large number of
> threads accessing it, and consumes a large amount of RAM.
> [~mikemccand] suggested the idea of a two array backed HPPC int->FacetLabel
> cache. The basic idea behind the cache being:
> # We use two hashmaps primary and secondary.
> # In case of a cache miss in the primary and a cache hit in the secondary,
> we add the key to the primary map as well.
> # In case of a cache miss in both the maps, we add it to the primary map.
> # When we reach (make this check each time we insert?) a large number of
> elements in say the primary cache, (say larger than the existing
> {color:#871094}DEFAULT_CACHE_VALUE{color}=4000), we dump the secondary map
> and copy all the values of the primary map into it.
> The idea was originally explained in
> [this|https://github.com/apache/lucene/pull/179#discussion_r692907559]
> comment.
>
>
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