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From Katherine Mora <KM...@searchtechnologies.com>
Subject ConcurrentModificationException due to high volume of requests
Date Fri, 12 Aug 2016 17:27:41 GMT
Hi All,

We are using Solr 5.2.1 in a production environment where we have a high volume of requests.
We are not having any timeouts or performance issues. However, the logs are filled with this
exception.
We've been researching and there isn't a lot of information about this problem or why it happens.
We have tried to reproduce it by sending queries using JMeter and it only happens when multiple
queries are sent at the same time.

Checking the code we found that this exception is within the core Solr code and part of the
exception caught our attention as it is logging debug information (we are using INFO logging
level) (org.apache.solr.search.stats.LocalStatsCache.get(LocalStatsCache.java:40)).

Has anyone seen this exception before? Would it be OK to generate a patch? We were thinking
about commenting the debug line or adding try/catch statements.

Thank you!


null:java.util.ConcurrentModificationException
         at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:394)
         at java.util.LinkedHashMap$EntryIterator.next(LinkedHashMap.java:413)
         at java.util.LinkedHashMap$EntryIterator.next(LinkedHashMap.java:412)
         at org.apache.solr.common.params.ModifiableSolrParams.toString(ModifiableSolrParams.java:201)
         at java.lang.String.valueOf(String.java:2849)
         at java.lang.StringBuilder.append(StringBuilder.java:128)
         at org.apache.solr.request.SolrQueryRequestBase.toString(SolrQueryRequestBase.java:165)
         at org.apache.solr.search.stats.LocalStatsCache.get(LocalStatsCache.java:40)
         at org.apache.solr.handler.component.QueryComponent.process(QueryComponent.java:366)
         at org.apache.solr.handler.component.SearchHandler.handleRequestBody(SearchHandler.java:255)
         at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:143)
         at org.apache.solr.core.SolrCore.execute(SolrCore.java:2064)
         at org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:654)
         at org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:450)
         at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:227)
         at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:196)
         at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
         at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)
         at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
         at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:577)
         at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223)
         at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
         at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
         at org.eclipse.jetty.server.handler.RequestLogHandler.handle(RequestLogHandler.java:95)
         at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1129)
         at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515)
         at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
         at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061)
         at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
         at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:215)
         at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:110)
         at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
         at org.eclipse.jetty.server.Server.handle(Server.java:497)
         at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:310)
         at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257)
         at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:540)
         at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
         at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
         at java.lang.Thread.run(Thread.java:745)


KATHERINE MORA
Senior Engineer


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