Package org.apache.hadoop.hbase.io.hfile

Interface HFileScanner

All Superinterfaces:
AutoCloseable, Closeable, Shipper
All Known Implementing Classes:
HFileReaderImpl.EncodedScanner, HFileReaderImpl.HFileScannerImpl
@Private public interface HFileScanner extends Shipper, Closeable
A scanner allows you to position yourself within a HFile and scan through it. It allows you to reposition yourself as well.

A scanner doesn't always have a key/value that it is pointing to when it is first created and before seekTo()/seekTo(ExtendedCell) are called. In this case, getKey()/getValue() returns null. At most other times, a key and value will be available. The general pattern is that you position the Scanner using the seekTo variants and then getKey and getValue.

  • Method Details

    • seekTo

      int seekTo(ExtendedCell cell) throws IOException
      SeekTo or just before the passed cell. Examine the return code to figure whether we found the cell or not. Consider the cell stream of all the cells in the file, c[0] .. c[n], where there are n cells in the file.
      Returns:
      -1, if cell < c[0], no position; 0, such that c[i] = cell and scanner is left in position i; and 1, such that c[i] < cell, and scanner is left in position i. The scanner will position itself between c[i] and c[i+1] where c[i] < cell <= c[i+1]. If there is no cell c[i+1] greater than or equal to the input cell, then the scanner will position itself at the end of the file and next() will return false when it is called.
      Throws:
      IOException

    • reseekTo

      int reseekTo(ExtendedCell cell) throws IOException
      Reseek to or just before the passed cell. Similar to seekTo except that this can be called even if the scanner is not at the beginning of a file. This can be used to seek only to cells which come after the current position of the scanner. Consider the cell stream of all the cells in the file, c[0] .. c[n], where there are n cellc in the file after current position of HFileScanner. The scanner will position itself between c[i] and c[i+1] where c[i] < cell <= c[i+1]. If there is no cell c[i+1] greater than or equal to the input cell, then the scanner will position itself at the end of the file and next() will return false when it is called.
      Parameters:
      cell - Cell to find (should be non-null)
      Returns:
      -1, if cell < c[0], no position; 0, such that c[i] = cell and scanner is left in position i; and 1, such that c[i] < cell, and scanner is left in position i.
      Throws:
      IOException

    • seekBefore

      boolean seekBefore(ExtendedCell cell) throws IOException
      Consider the cell stream of all the cells in the file, c[0] .. c[n], where there are n cells in the file.
      Parameters:
      cell - Cell to find
      Returns:
      false if cell <= c[0] or true with scanner in position 'i' such that: c[i] < cell. Furthermore: there may be a c[i+1], such that c[i] < cell <= c[i+1] but there may also NOT be a c[i+1], and next() will return false (EOF).
      Throws:
      IOException

    • seekTo

      boolean seekTo() throws IOException
      Positions this scanner at the start of the file.
      Returns:
      False if empty file; i.e. a call to next would return false and the current key and value are undefined.
      Throws:
      IOException

    • next

      boolean next() throws IOException
      Scans to the next entry in the file.
      Returns:
      Returns false if you are at the end otherwise true if more in file.
      Throws:
      IOException

    • getKey

      ExtendedCell getKey()
      Gets the current key in the form of a cell. You must call seekTo(ExtendedCell) before this method.
      Returns:
      gets the current key as a Cell.

    • getValue

      ByteBuffer getValue()
      Gets a buffer view to the current value. You must call seekTo(ExtendedCell) before this method.
      Returns:
      byte buffer for the value. The limit is set to the value size, and the position is 0, the start of the buffer view.

    • getCell

      ExtendedCell getCell()
      Returns Instance of ExtendedCell.

    • getReader

      HFile.Reader getReader()
      Returns Reader that underlies this Scanner instance.

    • isSeeked

      boolean isSeeked()
      Returns:
      True is scanner has had one of the seek calls invoked; i.e. seekBefore(ExtendedCell) or seekTo() or seekTo(ExtendedCell). Otherwise returns false.

    • getNextIndexedKey

      ExtendedCell getNextIndexedKey()
      Returns the next key in the index (the key to seek to the next block)

    • close

      void close()
      Close this HFile scanner and do necessary cleanup.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable

    • recordBlockSize

      void recordBlockSize(IntConsumer blockSizeConsumer)
      Record the size of the current block in bytes, passing as an argument to the blockSizeConsumer. Implementations should ensure that blockSizeConsumer is only called once per block.
      Parameters:
      blockSizeConsumer - to be called with block size in bytes, once per block.