我们使用Java8和AWSSDK以编程方式将文件上载到AWSS3。对于上传大文件（>100mb），我们了解到首选的方法是多部分上传。我们尝试过，但它似乎没有加快它，上传时间仍然几乎与不使用多部分上传相同。更糟糕的是，我们甚至遇到内存不足错误，称堆空间不足。
问题：
使用多部分上传真的应该加快上传速度吗？如果没有，为什么要使用它？
为什么使用多部分上传比不使用更快地消耗内存？它是否同时上传所有部分？
有关我们使用的代码，请参见下文：

private static void uploadFileToS3UsingBase64(String bucketName, String region, String accessKey, String secretKey,
        String fileBase64String, String s3ObjectKeyName) {
    byte[] bI = org.apache.commons.codec.binary.Base64.decodeBase64((fileBase64String.substring(fileBase64String.indexOf(",")+1)).getBytes());
    InputStream fis = new ByteArrayInputStream(bI);
    long start = System.currentTimeMillis();
    AmazonS3 s3Client = null;
    TransferManager tm = null;
    try {
        s3Client = AmazonS3ClientBuilder.standard().withRegion(region)
                .withCredentials(new AWSStaticCredentialsProvider(new BasicAWSCredentials(accessKey, secretKey)))
                .build();
        tm = TransferManagerBuilder.standard()
                  .withS3Client(s3Client)
                  .withMultipartUploadThreshold((long) (50* 1024 * 1025))
                  .build();
        ObjectMetadata metadata = new ObjectMetadata();
        metadata.setHeader(Headers.STORAGE_CLASS, StorageClass.Standard);
        PutObjectRequest putObjectRequest = new PutObjectRequest(bucketName, s3ObjectKeyName,
                fis, metadata).withSSEAwsKeyManagementParams(new SSEAwsKeyManagementParams());
        Upload upload = tm.upload(putObjectRequest);
        // Optionally, wait for the upload to finish before continuing.
        upload.waitForCompletion();
        long end = System.currentTimeMillis();
        long duration = (end - start)/1000;
        // Log status
        System.out.println("Successul upload in S3 multipart. Duration = " + duration);
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (s3Client != null)
            s3Client.shutdown();
        if (tm != null)
            tm.shutdownNow();
    }
}