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https://issues.apache.org/jira/browse/SOLR-14428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17090877#comment-17090877
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Mike Drob commented on SOLR-14428:
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Adding some notes here as I've been diving through this... The
queryResultsCache is built in
[SolrIndexSearcher|https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java#L278],
and uses a {{QueryResultKey}}, which stores the full {{Query}} object, which
in this case means the FuzzyQuery with the automata already built.
However, we don't really need to store the automata that we built, since they
aren't used for the equality comparison. Maybe there is an elegant way to store
a stripped down FuzzyQuery in the cache?
> FuzzyQuery has severe memory usage in 8.5
> -----------------------------------------
>
> Key: SOLR-14428
> URL: https://issues.apache.org/jira/browse/SOLR-14428
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 8.5, 8.5.1
> Reporter: Colvin Cowie
> Assignee: Andrzej Bialecki
> Priority: Major
> Attachments: FuzzyHammer.java, image-2020-04-23-09-18-06-070.png,
> screenshot-2.png, screenshot-3.png, screenshot-4.png
>
>
> I sent this to the mailing list
> I'm moving from 8.3.1 to 8.5.1, and started getting Out Of Memory Errors
> while running our normal tests. After profiling it was clear that the
> majority of the heap was allocated through FuzzyQuery.
> LUCENE-9068 moved construction of the automata from the FuzzyTermsEnum to the
> FuzzyQuery's constructor.
> I created a little test ( [^FuzzyHammer.java] ) that fires off fuzzy queries
> from random UUID strings for 5 minutes
> {code}
> FIELD_NAME + ":" + UUID.randomUUID().toString().replace("-", "") + "~2"
> {code}
> When running against a vanilla Solr 8.31 and 8.4.1 there is no problem, while
> the memory usage has increased drastically on 8.5.0 and 8.5.1.
> Comparison of heap usage while running the attached test against Solr 8.3.1
> and 8.5.1 with a single (empty) shard and 4GB heap:
> !image-2020-04-23-09-18-06-070.png!
> And with 4 shards on 8.4.1 and 8.5.0:
> !screenshot-2.png!
> I'm guessing that the memory might be being leaked if the FuzzyQuery objects
> are referenced from the cache, while the FuzzyTermsEnum would not have been.
> Query Result Cache on 8.5.1:
> !screenshot-3.png!
> ~316mb in the cache
> QRC on 8.3.1
> !screenshot-4.png!
> <1mb
> With an empty cache, running this query
> _field_s:e41848af85d24ac197c71db6888e17bc~2_ results in the following memory
> allocation
> {noformat}
> 8.3.1: CACHE.searcher.queryResultCache.ramBytesUsed: 1520
> 8.5.1: CACHE.searcher.queryResultCache.ramBytesUsed: 648855
> {noformat}
> ~1 gives 98253 and ~0 gives 6339 on 8.5.1. 8.3.1 is constant at 1520
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