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https://issues.apache.org/jira/browse/SOLR-13898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16972688#comment-16972688
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Yonik Seeley commented on SOLR-13898:
-------------------------------------
Using computeIfAbsent makes total sense for something like UnInvertedField,
which is huge and expensive and you absolutely don't want to ever build a
duplicate because of a race.
With something like the filter cache, the access pattern tends to be much
different and using computeIfAbsent can be optimizing for the rare case and not
the common case (well, the common case of 100% hit rate for the types of
requests that hit the filter cache many times and expect that hit rate to get
good performance... and on a miss, it's quick to compute anyway). All those
cases (variants of faceting, join, etc) are all requesting filters for terms
though, so perhaps that case could be handled differently from more complex
queries.
> Non-atomic use of SolrCache get / put
> -------------------------------------
>
> Key: SOLR-13898
> URL: https://issues.apache.org/jira/browse/SOLR-13898
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 8.3
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Major
> Fix For: 8.4
>
> Attachments: SOLR-13898.patch, SOLR-13898.patch
>
>
> As pointed out by [~ben.manes] in SOLR-13817 Solr code base in many key
> places uses a similar pattern of non-atomic get / put calls to SolrCache-s.
> In multi-threaded environment this leads to cache misses and additional
> unnecessary computations when competing threads both discover a missing
> value, non-atomically compute it and update the cache.
> Some of these places are known performance bottlenecks where efficient
> caching is especially important, such as {{SolrIndexSearcher}},
> {{SolrDocumentFetcher}}, {{UninvertedField}} and join queries .
> I propose to add {{SolrCache.computeIfAbsent(key, mappingFunction)}} that
> will atomically retrieve existing values or compute and update the cache.
> This will require also changing how the {{SolrCache.get(...)}} is used in
> many components.
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