Class: Innodb::Index::IndexCursor

Inherits:
Object
  • Object
show all
Defined in:
lib/innodb/index.rb

Overview

A cursor to walk the index (cursor) forwards or backward starting with a given record, or the minimum (:min) or maximum (:max) record in the index.

Instance Method Summary collapse

Constructor Details

#initialize(index, record, direction) ⇒ IndexCursor

Returns a new instance of IndexCursor.



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# File 'lib/innodb/index.rb', line 262

def initialize(index, record, direction)
  Innodb::Stats.increment :index_cursor_create
  @initial = true
  @index = index
  @direction = direction
  case record
  when :min
    # Start at the minimum record on the minimum page in the index.
    @page = index.min_page_at_level(0)
    @page_cursor = @page.record_cursor(:min, direction)
  when :max
    # Start at the maximum record on the maximum page in the index.
    @page = index.max_page_at_level(0)
    @page_cursor = @page.record_cursor(:max, direction)
  else
    # Start at the record provided.
    @page = record.page
    @page_cursor = @page.record_cursor(record.offset, direction)
  end
  @record = @page_cursor.record
end

Instance Method Details

#current_record ⇒ Object

Return the current record, mostly as a helper.



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# File 'lib/innodb/index.rb', line 285

def current_record
  @record
end

#each_record ⇒ Object

Iterate through all records in the cursor.



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# File 'lib/innodb/index.rb', line 352

def each_record
  unless block_given?
    return enum_for(:each_record)
  end

  while rec = record
    yield rec
  end
end

#next_record ⇒ Object

Move to the next record in the forward direction and return it.



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# File 'lib/innodb/index.rb', line 290

def next_record
  Innodb::Stats.increment :index_cursor_next_record

  while true
    if rec = @page_cursor.record
      return rec
    end

    unless next_page = @page.next
      return nil
    end

    unless @page = @index.page(next_page)
      raise "Failed to load next page"
    end

    unless @page_cursor = @page.record_cursor(:min, @direction)
      raise "Failed to position cursor"
    end
  end
end

#prev_record ⇒ Object

Move to the previous record in the backward direction and return it.



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# File 'lib/innodb/index.rb', line 313

def prev_record
  Innodb::Stats.increment :index_cursor_prev_record

  while true
    if rec = @page_cursor.record
      return rec
    end

    unless prev_page = @page.prev
      return nil
    end

    unless @page = @index.page(prev_page)
      raise "Failed to load prev page"
    end

    unless @page_cursor = @page.record_cursor(:max, @direction)
      raise "Failed to position cursor"
    end
  end
  raise "Not implemented"
end

#record ⇒ Object

Return the next record in the order defined when the cursor was created.



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# File 'lib/innodb/index.rb', line 337

def record
  if @initial
    @initial = false
    return current_record
  end

  case @direction
  when :forward
    next_record
  when :backward
    prev_record
  end
end