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https://issues.apache.org/jira/browse/CASSANDRA-8090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14175172#comment-14175172
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Benjamin Lerer commented on CASSANDRA-8090:
-------------------------------------------
With the fact that functions can be nested within functions you end up with a
tree structure of Selectors were each one of them might or might not need to
store some state.
The first approach to solve that problem is to use a Map to store the state and
to pass that map to each selector.
The problems that I see with that approach is that we will end up doing a lot
of map lookups (e.g. if we have 5 columns and 10 000 rows we will end up doing
50 000 map lookups). To avoid that performance cost I tried to have a state
container which is somehow iterable in the selector order but as the selectors
have a tree structure the result that I got was looking a bit hacky and it was
alway involving casting each time we were retrieving the state (which I found
quite ugly)
As we were any way forced to create the same (or a bit less) number of state
objects than selectors I choosed to keep the state and the method together and
to create a new set of selectors each time but for that I needed a factory.
> NullPointerException when using prepared statements
> ---------------------------------------------------
>
> Key: CASSANDRA-8090
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8090
> Project: Cassandra
> Issue Type: Bug
> Reporter: Carl Yeksigian
> Assignee: Benjamin Lerer
> Fix For: 3.0
>
>
> Due to the changes in CASSANDRA-4914, using a prepared statement from
> multiple threads leads to a race condition where the simple selection may be
> reset from a different thread, causing the following NPE:
> {noformat}
> java.lang.NullPointerException: null
> at org.apache.cassandra.cql3.ResultSet.addRow(ResultSet.java:63)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.Selection$ResultSetBuilder.build(Selection.java:372)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.SelectStatement.process(SelectStatement.java:1120)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.SelectStatement.processResults(SelectStatement.java:283)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.SelectStatement.execute(SelectStatement.java:260)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.SelectStatement.execute(SelectStatement.java:213)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.statements.SelectStatement.execute(SelectStatement.java:63)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.QueryProcessor.processStatement(QueryProcessor.java:226)
> ~[main/:na]
> at
> org.apache.cassandra.cql3.QueryProcessor.processPrepared(QueryProcessor.java:481)
> ~[main/:na]
> at
> org.apache.cassandra.transport.messages.ExecuteMessage.execute(ExecuteMessage.java:133)
> ~[main/:na]
> at
> org.apache.cassandra.transport.Message$Dispatcher.channelRead0(Message.java:438)
> [main/:na]
> at
> org.apache.cassandra.transport.Message$Dispatcher.channelRead0(Message.java:334)
> [main/:na]
> at
> io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
> [netty-all-4.0.23.Final.jar:4.0.23.Final]
> at
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
> [netty-all-4.0.23.Final.jar:4.0.23.Final]
> at
> io.netty.channel.AbstractChannelHandlerContext.access$700(AbstractChannelHandlerContext.java:32)
> [netty-all-4.0.23.Final.jar:4.0.23.Final]
> at
> io.netty.channel.AbstractChannelHandlerContext$8.run(AbstractChannelHandlerContext.java:324)
> [netty-all-4.0.23.Final.jar:4.0.23.Final]
> at
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
> [na:1.7.0_67]
> at
> org.apache.cassandra.concurrent.AbstractTracingAwareExecutorService$FutureTask.run(AbstractTracingAwareExecutorService.java:163)
> [main/:na]
> at org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:103)
> [main/:na]
> at java.lang.Thread.run(Thread.java:745) [na:1.7.0_67]
> {noformat}
> Reproduced this using the stress tool:
> {noformat}
> ./tools/bin/cassandra-stress user profile=tools/cqlstress-example.yaml
> ops\(insert=1,simple1=1\)
> {noformat}
> You'll need to change the {noformat}select:{noformat} line to be /1000 to
> prevent the illegal query exceptions.
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