Method: PEROBS::BTree#initialize

Defined in:
lib/perobs/BTree.rb

#initialize(dir, name, order, progressmeter) ⇒ BTree

Create a new BTree object.

Parameters:

  • dir (String) —

    Directory to store the tree file

  • name (String) —

    Base name of the BTree related files in ‘dir’

  • order (Integer) —

    The maximum number of keys per node. This number must be odd and larger than 2 and smaller than 2**16 - 1.

  • progressmeter (ProgressMeter) —

    reference to a ProgressMeter object



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# File 'lib/perobs/BTree.rb', line 51

def initialize(dir, name, order, progressmeter)
  @dir = dir
  @name = name
  @progressmeter = progressmeter

  unless order > 4
    PEROBS.log.fatal "BTree order must be larger than 4, not #{order}"
  end
  unless order % 2 == 1
    PEROBS.log.fatal "BTree order must be an uneven number, not #{order}"
  end
  unless order < 2 ** 16 - 1
    PEROBS.log.fatal "BTree order must be smaller than #{2**16 - 1}"
  end
  @order = order

  # This EquiBlobsFile contains the nodes of the BTree.
  @nodes = EquiBlobsFile.new(@dir, @name, @progressmeter,
                             BTreeNode::node_bytes(@order))
  @nodes.register_custom_data('first_leaf')
  @nodes.register_custom_data('last_leaf')
  @nodes.register_custom_data('btree_size')
  @node_cache = PersistentObjectCache.new(2**16, -1, BTreeNode, self)
  @root = @first_leaf = @last_leaf = nil
  @size = 0

  # This BTree implementation uses a write cache to improve write
  # performance of multiple successive read/write operations. This also
  # means that data may not be written on the backing store until the
  # sync() or close() methods have been called. A bug in the program or a
  # premature program termination can lead to data loss. To detect such
  # situations, we use a lock file whenever there are pending writes.
  @is_dirty = false
  @dirty_flag = LockFile.new(File.join(@dir, name + '.dirty'),
                             { :timeout_secs => 0 })
end