presto-main/src/main/java/io/prestosql/operator/ChannelSet.java/ChannelSet/updateMemoryReservation
class ChannelSet:        public boolean updateMemoryReservation()
        {
            // If memory is not available, once we return, this operator will be blocked until memory is available.
            localMemoryContext.setBytes(hash.getEstimatedSize());

            // If memory is not available, inform the caller that we cannot proceed for allocation.
            return operatorContext.isWaitingForMemory().isDone();
        }