Changes to RandomAccessFile in jdk9

[Ismael Juma]

Hi all,

I'm a Kafka committer and noticed this discussion. Kafka uses
RandomAccessFile.setLength in two places.

For the memory mapped index files:

protected var mmap: MappedByteBuffer = {
    val newlyCreated = file.createNewFile()
    val raf = if (writable) new RandomAccessFile(file, "rw") else new
RandomAccessFile(file, "r")
    try {
      /* pre-allocate the file if necessary */
      if(newlyCreated) {
        if(maxIndexSize < entrySize)
          throw new IllegalArgumentException("Invalid max index size: " +
maxIndexSize)
        raf.setLength(roundDownToExactMultiple(maxIndexSize, entrySize))
      }

      /* memory-map the file */
      _length = raf.length()
      val idx = {
        if (writable)
          raf.getChannel.map(FileChannel.MapMode.READ_WRITE, 0, _length)
        else
          raf.getChannel.map(FileChannel.MapMode.READ_ONLY, 0, _length)
      }
      /* set the position in the index for the next entry */
      if(newlyCreated)
        idx.position(0)
      else
        // if this is a pre-existing index, assume it is valid and set
position to last entry
        idx.position(roundDownToExactMultiple(idx.limit(), entrySize))
      idx
    } finally {
      CoreUtils.swallow(raf.close(), this)
    }
  }

For the log segment files (written sequentially via FileChannel) if
preallocate is true:

    /**
     * Open a channel for the given file
     * For windows NTFS and some old LINUX file system, set preallocate to
true and initFileSize
     * with one value (for example 512 * 1025 *1024 ) can improve the kafka
produce performance.
     * @param file File path
     * @param mutable mutable
     * @param fileAlreadyExists File already exists or not
     * @param initFileSize The size used for pre allocate file, for example
512 * 1025 *1024
     * @param preallocate Pre-allocate file or not, gotten from
configuration.
     */
    private static FileChannel openChannel(File file,
                                           boolean mutable,
                                           boolean fileAlreadyExists,
                                           int initFileSize,
                                           boolean preallocate) throws
IOException {
        if (mutable) {
            if (fileAlreadyExists) {
                return new RandomAccessFile(file, "rw").getChannel();
            } else {
                if (preallocate) {
                    RandomAccessFile randomAccessFile = new
RandomAccessFile(file, "rw");
                    randomAccessFile.setLength(initFileSize);
                    return randomAccessFile.getChannel();
                } else {
                    return new RandomAccessFile(file, "rw").getChannel();
                }
            }
        } else {
            return new FileInputStream(file).getChannel();
        }
    }

Enrico, the change in behaviour you have seen is for the index files? I
suspect so as `preallocate` is only typically enabled by Windows users.

Ismael

On Fri, Apr 20, 2018 at 6:50 AM, Alan Bateman <Alan.Bateman at oracle.com>
wrote:

> On 20/04/2018 13:09, Enrico Olivelli wrote:
>
>>
>> Alan, Ivan
>> Thank you for spending time on this.
>>
>> Do you think there will be some change (change to previous behavior) or
>> simply some consolidation on current behavior (docs, tests in the codebase)?
>>
>> Should I file some issue on the bugtracker?
>>
> I'm confident that Ivan is correct (I have forgotten this was fixed in
> RandomAccessFile at the same time as FileChannel). So it is a deliberate
> change and one that should probably have had a release note.
>
> -Alan
>
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