Subqueries in Single Stage Engine fail with NPE if OOM protection is on.

[vrajat]

A reproducer is available in master...vrajat:rv-oom-subquery-npe

The issue is that subqueries make recursive calls to BaseSingleStageBrokerRequestHandler.handleRequest. The inner call clears the tracing context. When the outer call runs the reducer, no context is found and an NPE is thrown.

Stack Trace:

java.lang.NullPointerException: Cannot invoke "org.apache.pinot.spi.accounting.ThreadResourceUsageProvider.getThreadAllocatedBytes()" because the return value of "org.apache.pinot.core.accounting.PerQueryCPUMemAccountantFactory$PerQueryCPUMemResourceUsageAccountant.getThreadResourceUsageProvider()" is null
	at org.apache.pinot.core.accounting.PerQueryCPUMemAccountantFactory$PerQueryCPUMemResourceUsageAccountant.sampleThreadBytesAllocated(PerQueryCPUMemAccountantFactory.java:294) ~[classes/:?]
	at org.apache.pinot.core.accounting.PerQueryCPUMemAccountantFactory$PerQueryCPUMemResourceUsageAccountant.sampleUsage(PerQueryCPUMemAccountantFactory.java:238) ~[classes/:?]
	at org.apache.pinot.spi.trace.Tracing$ThreadAccountantOps.sample(Tracing.java:311) ~[classes/:?]
	at org.apache.pinot.spi.trace.Tracing$ThreadAccountantOps.sampleAndCheckInterruption(Tracing.java:352) ~[classes/:?]
	at org.apache.pinot.core.query.reduce.AggregationDataTableReducer.reduceWithIntermediateResult(AggregationDataTableReducer.java:88) ~[classes/:?]
	at org.apache.pinot.core.query.reduce.AggregationDataTableReducer.reduceAndSetResults(AggregationDataTableReducer.java:79) ~[classes/:?]
	at org.apache.pinot.core.query.reduce.BrokerReduceService.reduceOnDataTable(BrokerReduceService.java:159) ~[classes/:?]
	at org.apache.pinot.broker.requesthandler.SingleConnectionBrokerRequestHandler.processBrokerRequest(SingleConnectionBrokerRequestHandler.java:149) ~[classes/:?]
	at org.apache.pinot.broker.requesthandler.BaseSingleStageBrokerRequestHandler.handleRequest(BaseSingleStageBrokerRequestHandler.java:838) ~[classes/:?]
	at org.apache.pinot.broker.requesthandler.BaseBrokerRequestHandler.handleRequest(BaseBrokerRequestHandler.java:193) ~[classes/:?]
	at org.apache.pinot.broker.requesthandler.BrokerRequestHandlerDelegate.handleRequest(BrokerRequestHandlerDelegate.java:116) ~[classes/:?]
	at org.apache.pinot.broker.api.resources.PinotClientRequest.executeSqlQuery(PinotClientRequest.java:490) ~[classes/:?]
	at org.apache.pinot.broker.api.resources.PinotClientRequest.processSqlQueryPost(PinotClientRequest.java:177) ~[classes/:?]
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[?:?]
	at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[?:?]