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https://issues.apache.org/jira/browse/SOLR-17863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18015485#comment-18015485
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ASF subversion and git services commented on SOLR-17863:
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Commit 764aff6cf5d5a3827a2c1376c5c89719abf86d21 in solr's branch
refs/heads/branch_9x from Luke Kot-Zaniewski
[ https://gitbox.apache.org/repos/asf?p=solr.git;h=764aff6cf5d ]
SOLR-17863: fix per segment fingerprint cache race (#3477)
Fix race condition in SolrCore's fingerprint cache which caused leader election
to hang
> SolrCore's perSegmentFingerprintCache Is Not Thread-safe
> --------------------------------------------------------
>
> Key: SOLR-17863
> URL: https://issues.apache.org/jira/browse/SOLR-17863
> Project: Solr
> Issue Type: Bug
> Affects Versions: 9.3, 9.8.1
> Reporter: Luke Kot-Zaniewski
> Priority: Critical
> Labels: pull-request-available
> Attachments: image-2025-08-14-11-29-04-739.png,
> image-2025-08-14-11-29-42-832.png
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> SOLR-16713 introduced a race condition into the perSegmentFingerprintCache as
> it changed it from the [thread-safe guava implementation to the thread-UNSAFE
> WeakHashMap|https://github.com/apache/solr/commit/375ac647ad507638686848c549c30e6c077dca1b#diff-3bf44f923643744a743460bb0f64301618dd7529a602d945fe2f7f193d4cdde0].
> This flew under the radar for some time because this map previously had very
> little contention between threads. However after SOLR-17756 we turbo-charged
> the race after parallelizing at a much more granular level upstream of this
> call. The net effect is that WeakHashMap:put can get stuck in an
> infinite-loop (probably due to a cycle in the underlying linked-list that it
> modifies):
> !image-2025-08-14-11-29-04-739.png!
> !image-2025-08-14-11-29-42-832.png!
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