Class BlockedByteArray

java.lang.Object
org.apache.derby.impl.io.vfmem.BlockedByteArray
public class BlockedByteArray extends Object
Stores data in blocks, and supports reading/writing data from/into these blocks.

The blocked array is expanded and shrunk as required.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private static final int
    _16K
    Constant for 16 KB.
    private static final int
    _32K
    Constant for 32 KB.
    private static final int
    _4K
    Constant for 4 KB.
    private static final int
    _8K
    Constant for 8 KB.
    private int
    allocatedBlocks
    The number of allocated blocks.
    private byte[][]
    blocks
    References to blocks of data.
    private int
    blockSize
    The size of a block of data (the allocation unit).
    private static final int
    DEFAULT_BLOCKSIZE
    The default block size.
    private static final int
    INITIAL_BLOCK_HOLDER_SIZE
    The default number of slots for holding a block of data.
    private long
    length
    The number of bytes stored in the blocked byte array.
    private static final int
    MIN_HOLDER_GROWTH
    Minimum number of holder slots to grow with when the block holder array has to grow to be able to reference all the data arrays.

  • Constructor Summary

    Constructors
    Constructor
    Description
    BlockedByteArray()
    Creates a new blocked byte array with the default number of slots to hold byte arrays (blocks).

  • Method Summary

    Modifier and Type
    Method
    Description
    private void
    checkBlockSize(int len)
    Tries to optimize the block size by setting it equal to the the page size used by the database.
    (package private) BlockedByteArrayInputStream
    getInputStream()
    Returns an input stream serving the data in the blocked byte array.
    (package private) BlockedByteArrayOutputStream
    getOutputStream(long pos)
    Returns an output stream writing data into the blocked byte array.
    private void
    increaseCapacity(long lastIndex)
    Increases the capacity of this blocked byte array by allocating more blocks.
    long
    length()
    Returns the number of bytes allocated.
    int
    read(long pos)
    Returns the byte at the given position.
    int
    read(long pos, byte[] buf, int offset, int len)
    Reads up to len bytes.
    (package private) void
    release()
    Releases this array.
    void
    setLength(long newLength)
    Changes the allocated length of the data.
    int
    writeByte(long pos, byte b)
    Writes the given byte into the blocked byte array.
    int
    writeBytes(long pos, byte[] buf, int offset, int len)
    Writes the given bytes into the blocked byte array.

    Methods inherited from class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • _4K

      private static final int _4K
      Constant for 4 KB.
      See Also:

    • _8K

      private static final int _8K
      Constant for 8 KB.
      See Also:

    • _16K

      private static final int _16K
      Constant for 16 KB.
      See Also:

    • _32K

      private static final int _32K
      Constant for 32 KB.
      See Also:

    • DEFAULT_BLOCKSIZE

      private static final int DEFAULT_BLOCKSIZE
      The default block size.
      See Also:

    • INITIAL_BLOCK_HOLDER_SIZE

      private static final int INITIAL_BLOCK_HOLDER_SIZE
      The default number of slots for holding a block of data.
      See Also:

    • MIN_HOLDER_GROWTH

      private static final int MIN_HOLDER_GROWTH
      Minimum number of holder slots to grow with when the block holder array has to grow to be able to reference all the data arrays.
      See Also:

    • blocks

      private byte[][] blocks
      References to blocks of data.

    • blockSize

      private int blockSize
      The size of a block of data (the allocation unit).

    • allocatedBlocks

      private int allocatedBlocks
      The number of allocated blocks.

    • length

      private long length
      The number of bytes stored in the blocked byte array.

  • Constructor Details

    • BlockedByteArray

      public BlockedByteArray()
      Creates a new blocked byte array with the default number of slots to hold byte arrays (blocks).

      No blocks are pre-allocated.

      See Also:

  • Method Details

    • read

      public int read(long pos)
      Returns the byte at the given position.
      Parameters:
      pos - position to read from
      Returns:
      A single byte.

    • read

      public int read(long pos, byte[] buf, int offset, int len)
      Reads up to len bytes.
      Parameters:
      pos - the position to start reading at
      buf - the destination buffer
      offset - offset into the destination buffer
      len - the number of bytes to read
      Returns:
      The number of bytes read.

    • length

      public long length()
      Returns the number of bytes allocated.
      Returns:
      Bytes allocated.

    • setLength

      public void setLength(long newLength)
      Changes the allocated length of the data.

      If the new length is larger than the current length, the blocked byte array will be extended with new blocks. If the new length is smaller, existing (allocated) blocks will be removed if possible.

      Parameters:
      newLength - the new length of the allocated data in bytes

    • writeBytes

      public int writeBytes(long pos, byte[] buf, int offset, int len)
      Writes the given bytes into the blocked byte array.
      Parameters:
      pos - the position to start writing at
      buf - the source buffer
      offset - the offset into the source buffer
      len - the number of bytes to write
      Returns:
      The number of bytes written.

    • writeByte

      public int writeByte(long pos, byte b)
      Writes the given byte into the blocked byte array.
      Parameters:
      pos - the position to write the byte at
      b - the byte to write
      Returns:
      1, which is the number of bytes written.

    • getInputStream

      BlockedByteArrayInputStream getInputStream()
      Returns an input stream serving the data in the blocked byte array.
      Returns:
      An InputStream-object.

    • getOutputStream

      BlockedByteArrayOutputStream getOutputStream(long pos)
      Returns an output stream writing data into the blocked byte array.
      Parameters:
      pos - initial position of the output stream
      Returns:
      An OutputStream-object.

    • release

      void release()
      Releases this array.

    • checkBlockSize

      private void checkBlockSize(int len)
      Tries to optimize the block size by setting it equal to the the page size used by the database.

      Since we don't have a way of knowing which page size will be used, wait to set the block size until the first write request and see how many bytes are written then.

      Parameters:
      len - the requested number of bytes to be written

    • increaseCapacity

      private void increaseCapacity(long lastIndex)
      Increases the capacity of this blocked byte array by allocating more blocks.
      Parameters:
      lastIndex - the index that must fit into the array