[CASSANDRA-5382] ConcurrentModificantionException on server when multiple CQL3 read requests received on single column family simultaneously.

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 1.2.4

Environment

SLES, Sun JDK 1.6.0_43

• Severity: Low
• Assignee: Sylvain Lebresne
• Reporter: Jason Reber

Authors

Sylvain Lebresne

Reviewers

Jonathan Ellis

• Created: 25/Mar/13 16:24
• Updated: 16/Apr/19 09:32
• Resolved: 27/Mar/13 10:42

Description

The exception below is thrown on the server when two reads are performed at the exact same time on the same column family. This causes the query to fail.

The problem appears to be caused by the 'name' list in org.apache.cassandra.cql3.ResultSet$Metadata. The reference is passed in to the constructor and iterated without copying and without a synch block. When two of these ResultSet instances are created from the same metadata list at the same time, a ConcurrentModificationException is thrown.

The error:

ERROR [Thrift:860] 2013-03-25 09:27:39,467 CustomTThreadPoolServer.java (line 217) Error occurred during processing of message.
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at org.apache.cassandra.cql3.ResultSet$Metadata.allInSameCF(ResultSet.java:237)
at org.apache.cassandra.cql3.ResultSet$Metadata.<init>(ResultSet.java:219)
at org.apache.cassandra.cql3.ResultSet.<init>(ResultSet.java:47)
at org.apache.cassandra.cql3.statements.Selection$ResultSetBuilder.<init>(Selection.java:239)
at org.apache.cassandra.cql3.statements.Selection$ResultSetBuilder.<init>(Selection.java:221)
at org.apache.cassandra.cql3.statements.Selection.resultSetBuilder(Selection.java:211)
at org.apache.cassandra.cql3.statements.SelectStatement.process(SelectStatement.java:655)
at org.apache.cassandra.cql3.statements.SelectStatement.processResults(SelectStatement.java:147)
at org.apache.cassandra.cql3.statements.SelectStatement.execute(SelectStatement.java:136)
at org.apache.cassandra.cql3.statements.SelectStatement.execute(SelectStatement.java:62)
at org.apache.cassandra.cql3.QueryProcessor.processStatement(QueryProcessor.java:132)
at org.apache.cassandra.cql3.QueryProcessor.processPrepared(QueryProcessor.java:254)
at org.apache.cassandra.thrift.CassandraServer.execute_prepared_cql3_query(CassandraServer.java:1851)
at org.apache.cassandra.thrift.Cassandra$Processor$execute_prepared_cql3_query.getResult(Cassandra.java:4166)
at org.apache.cassandra.thrift.Cassandra$Processor$execute_prepared_cql3_query.getResult(Cassandra.java:4154)
at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:32)
at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:34)
at org.apache.cassandra.thrift.CustomTThreadPoolServer$WorkerProcess.run(CustomTThreadPoolServer.java:199)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)