presto-main/src/main/java/io/prestosql/execution/buffer/OutputBufferMemoryManager.java/OutputBufferMemoryManager/onMemoryAvailable
class OutputBufferMemoryManager:    @VisibleForTesting
    synchronized void onMemoryAvailable()
    {
        // Do not notify the listeners if the buffer is full
        if (bufferedBytes.get() > maxBufferedBytes) {
            return;
        }

        // notify listeners if the buffer is not full
        SettableFuture<?> future = this.bufferBlockedFuture;
        notificationExecutor.execute(() -> future.set(null));
    }