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From "Ben Manes (Jira)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-13898) Non-atomic use of SolrCache get / put
Date Tue, 19 Nov 2019 15:23:00 GMT

    [ https://issues.apache.org/jira/browse/SOLR-13898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16977551#comment-16977551
] 

Ben Manes commented on SOLR-13898:
----------------------------------

Caffeine has a little randomness in its eviction policy to protect from HashDoS style of attacks.
This means you may see very small differences between runs, even in a single threaded case.
Your test is already non deterministic due to concurrency, so both could explain the slight
differences.

> 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, 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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