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From "Andrzej Bialecki (Jira)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-13898) Non-atomic use of SolrCache get / put
Date Tue, 12 Nov 2019 20:14:00 GMT

    [ https://issues.apache.org/jira/browse/SOLR-13898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16972740#comment-16972740
] 

Andrzej Bialecki commented on SOLR-13898:
-----------------------------------------

Yeah, at this point I'm not very concerned about legacy caches, but until they are removed
I'd prefer them to at least behave correctly, even if they're not the most efficient.

I briefly looked at how caches are accessed and populated in {{SolrIndexSearcher}} and I'm
not comfortable touching this code, except in a few obvious places (I'll update the patch
in a moment).

I noticed that {{UnifiedHighlighter}} uses {{SolrIndexSearcher.doc(id, visitor)}}, which in
turn delegates to {{SolrDocumentFetcher.doc(id, visitor)}}, which does not use cache. Is this
on purpose? I would expect highlighting to benefit from caching ...

> 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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