Description of problem:
The metrics aggregation that is run during the DataPurgeJob will deadlock on a single processor (having only a single core) machine. The thread pool size used during aggregation is configured as follows,

private int numAggregationWorkers = Math.min(Integer.parseInt(System.getProperty("rhq.metrics.aggregation.workers",
        "4")), Runtime.getRuntime().availableProcessors());

If Runtime.getRuntime().availableProcessors() returns a value of one, then the aggregation will deadlock. BatchAggregationScheduler runs as a thread pool task. It queries metrics_index and schedules aggregation tasks. Reads are throttled using a Semaphore. The relevant code looks like,

for (Row row : rows) {
    aggregationState.getPermits().acquire();
    // schedule tasks...
}

Permits are released by the tasks that get scheduled. With a single thread, those tasks will not run until BatchAggregationScheduler finishes, and it will block indefinitely once there are no more permits.

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