Bug: Fix concurrent access of ClientWarn causing AIOBE for SELECT WHERE IN queries with multiple coordinator-local partitions
Status: Resolved
Priority: Normal
Resolution: Fixed
Created: 23/Feb/24 15:23
Resolved: 29/Feb/24 11:11

On one of our clusters, we noticed rare but periodic ArrayIndexOutOfBoundsExceptions:

 
{code:java}
message="Uncaught exception on thread Thread[ReadStage-3,5,main]"
exception="java.lang.RuntimeException: java.lang.ArrayIndexOutOfBoundsException
at org.apache.cassandra.service.StorageProxy$DroppableRunnable.run(StorageProxy.java:2579)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$FutureTask.run(AbstractLocalAwareExecutorService.java:162)
at org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$LocalSessionFutureTask.run(AbstractLocalAwareExecutorService.java:134)
at org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:119)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.ArrayIndexOutOfBoundsException"{code}
 

 

The error was in a Runnable, so the stacktrace didn't directly indicate where the error was coming from. We enabled JFR to log the underlying exception that was thrown:
 
{code:java}
message="Uncaught exception on thread Thread[ReadStage-2,5,main]" exception="java.lang.RuntimeException: java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 0
at org.apache.cassandra.service.StorageProxy$DroppableRunnable.run(StorageProxy.java:2579)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$FutureTask.run(AbstractLocalAwareExecutorService.java:162)
at org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$LocalSessionFutureTask.run(AbstractLocalAwareExecutorService.java:134)
at org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:119)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 0
at java.base/java.util.ArrayList.add(ArrayList.java:487)
at java.base/java.util.ArrayList.add(ArrayList.java:499)
at org.apache.cassandra.service.ClientWarn$State.add(ClientWarn.java:84)
at org.apache.cassandra.service.ClientWarn$State.access$000(ClientWarn.java:77)
at org.apache.cassandra.service.ClientWarn.warn(ClientWarn.java:51)
at org.apache.cassandra.db.ReadCommand$1MetricRecording.onClose(ReadCommand.java:596)
at org.apache.cassandra.db.transform.BasePartitions.runOnClose(BasePartitions.java:70)
at org.apache.cassandra.db.transform.BaseIterator.close(BaseIterator.java:95)
at org.apache.cassandra.service.StorageProxy$LocalReadRunnable.runMayThrow(StorageProxy.java:2260)
at org.apache.cassandra.service.StorageProxy$DroppableRunnable.run(StorageProxy.java:2575)
... 6 more"{code}
 
 

An AIOBE on ArrayList.add(E) should only be possible when multiple threads attempt to call the method at the same time.

 

This was seen while executing a SELECT WHERE IN query with multiple partition keys. This exception could happen when multiple local reads are dispatched by the coordinator in org.apache.cassandra.service.reads.AbstractReadExecutor#makeRequests. In this case, multiple local reads exceed the tombstone warning threshold, so multiple tombstone warnings are added to the same ClientWarn.State reference.  Currently, org.apache.cassandra.service.ClientWarn.State#warnings is an ArrayList, which isn't safe for concurrent modification, causing the AIOBE to be thrown.

 

I have a patch available for this, and I'm preparing it now. The patch is simple - it just changes org.apache.cassandra.service.ClientWarn.State#warnings to a thread-safe CopyOnWriteArrayList. I also have a jvm-dtest that demonstrates the issue but doesn't need to be merged - it shows how a SELECT WHERE IN query with local reads that add client warnings can add to the same ClientWarn.State from different threads. I'll push that in a separate branch just for demonstration purposes.

 

Demonstration branch: [https://github.com/apache/cassandra/compare/trunk...aratno:cassandra:CASSANDRA-19427-aiobe-clientwarn-demo]

Fix branch: [https://github.com/apache/cassandra/compare/trunk...aratno:cassandra:CASSANDRA-19427-aiobe-clientwarn-fix] (PR linked below)

 

This appears to have been an issue since at least 3.11, that was the earliest release I checked.