presto-main/src/main/java/io/prestosql/execution/buffer/LazyOutputBuffer.java/LazyOutputBuffer/isOverutilized
class LazyOutputBuffer:    @Override
    public boolean isOverutilized()
    {
        OutputBuffer outputBuffer;
        synchronized (this) {
            outputBuffer = delegate;
        }

        // until output buffer is initialized, readers cannot enqueue and thus cannot be blocked
        return (outputBuffer != null) && outputBuffer.isOverutilized();
    }