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https://issues.apache.org/jira/browse/SOLR-17413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17945729#comment-17945729
 ] 

ASF subversion and git services commented on SOLR-17413:
--------------------------------------------------------

Commit 3dd3a96f09c89f5d6a9f2915256aface46a4a8a0 in solr's branch 
refs/heads/add-pki-caching from Jason Gerlowski
[ https://gitbox.apache.org/repos/asf?p=solr.git;h=3dd3a96f09c ]

SOLR-17413: ulog replay should copy SolrQueryRequest (#110)

SolrQueryRequest is a non-threadsafe type, but was being shared across
executor threads during UpdateLog replay.  This introduces a number of
issues, not the least being a ConcurrentModificationException if
multiple threads happen to tweak the request 'context' simultaneously.

This commit fixes this issue by giving each executor thread a unique
LocalSolrQueryRequest instance to use.

NOTE: This fix is on its way to 9.8 upstream, but may take a slightly
different final form.

Co-authored-by: Jason Gerlowski <gerlowsk...@apache.org>

> UpdateLog Replay can throw ConcurrentModificationException from sharing the 
> request
> -----------------------------------------------------------------------------------
>
>                 Key: SOLR-17413
>                 URL: https://issues.apache.org/jira/browse/SOLR-17413
>             Project: Solr
>          Issue Type: Bug
>            Reporter: David Smiley
>            Assignee: Jason Gerlowski
>            Priority: Major
>              Labels: newdev, pull-request-available
>             Fix For: 9.8
>
>          Time Spent: 1h 50m
>  Remaining Estimate: 0h
>
> I saw org.apache.solr.cloud.BasicDistributedZkTest fail with a stack trace 
> revealing we have a real issue with UpdateLog replay.  Essentially, a 
> SolrQueryRequest is not threadsafe but we replay logs in parallel sharing the 
> same request instance.  Creating DistributedUpdateProcessor ends up adding to 
> a shared HashMap in req.getContext() that should not be shared.
> {noformat}
>   2> WARNING: Uncaught exception in thread: 
> Thread[replayUpdatesExecutor-590-thread-2,5,TGRP-BasicDistributedZkTest]
>   2> java.util.ConcurrentModificationException
>   2>  at __randomizedtesting.SeedInfo.seed([F2227B12A8FC234]:0)
>   2>  at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1135)
>   2>  at 
> org.apache.solr.update.processor.DistributedUpdateProcessorFactory.addParamToDistributedRequestWhitelist(DistributedUpdateProcessorFactory.java:46)
>   2>  at 
> org.apache.solr.update.processor.DistributedUpdateProcessor.<init>(DistributedUpdateProcessor.java:190)
>   2>  at 
> org.apache.solr.update.processor.DistributedUpdateProcessor.<init>(DistributedUpdateProcessor.java:160)
>   2>  at 
> org.apache.solr.update.processor.DistributedZkUpdateProcessor.<init>(DistributedZkUpdateProcessor.java:114)
>   2>  at 
> org.apache.solr.update.processor.DistributedUpdateProcessorFactory.getInstance(DistributedUpdateProcessorFactory.java:59)
>   2>  at 
> org.apache.solr.update.processor.UpdateRequestProcessorChain.createProcessor(UpdateRequestProcessorChain.java:242)
>   2>  at 
> org.apache.solr.update.processor.UpdateRequestProcessorChain.createProcessor(UpdateRequestProcessorChain.java:214)
>   2>  at 
> org.apache.solr.update.UpdateLog$LogReplayer.lambda$doReplay$0(UpdateLog.java:2103)
>   2>  at 
> java.base/java.lang.ThreadLocal$SuppliedThreadLocal.initialValue(ThreadLocal.java:305)
>   2>  at java.base/java.lang.ThreadLocal.setInitialValue(ThreadLocal.java:195)
>   2>  at java.base/java.lang.ThreadLocal.get(ThreadLocal.java:172)
>   2>  at 
> org.apache.solr.update.UpdateLog$LogReplayer.lambda$execute$2(UpdateLog.java:2342)
>   2>  at 
> org.apache.solr.util.OrderedExecutor.lambda$execute$0(OrderedExecutor.java:68)
>   2>  at 
> org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor.lambda$execute$1(ExecutorUtil.java:449)
>   2>  at 
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
>   2>  at 
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
>   2>  at java.base/java.lang.Thread.run(Thread.java:829)
> {noformat}



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