Class: Innodb::Page::Index::RecordCursor

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

Overview

A class for cursoring through records starting from an arbitrary point.

Instance Method Summary collapse

Constructor Details

#initialize(page, offset, direction) ⇒ RecordCursor

Returns a new instance of RecordCursor.



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# File 'lib/innodb/page/index.rb', line 715

def initialize(page, offset, direction)
  Innodb::Stats.increment :page_record_cursor_create

  @initial = true
  @page = page
  @direction = direction
  @record = initial_record(offset)
end

Instance Method Details

#each_record ⇒ Object

Iterate through all records in the cursor.



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# File 'lib/innodb/page/index.rb', line 789

def each_record
  return enum_for(:each_record) unless block_given?

  while (rec = record)
    yield rec
  end
end

#initial_record(offset) ⇒ Object 



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# File 'lib/innodb/page/index.rb', line 724

def initial_record(offset)
  case offset
  when :min
    @page.min_record
  when :max
    @page.max_record
  else
    # Offset is a byte offset of a record (hopefully).
    @page.record(offset)
  end
end

#next_record ⇒ Object

Return the next record, and advance the cursor. Return nil when the end of records (supremum) is reached.



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# File 'lib/innodb/page/index.rb', line 738

def next_record
  Innodb::Stats.increment :page_record_cursor_next_record

  rec = @page.record(@record.next)

  # The garbage record list's end is self-linked, so we must check for
  # both supremum and the current record's offset.
  if rec == @page.supremum || rec.offset == @record.offset
    # We've reached the end of the linked list at supremum.
    nil
  else
    @record = rec
  end
end

#prev_record ⇒ Object

Return the previous record, and advance the cursor. Return nil when the end of records (infimum) is reached.



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# File 'lib/innodb/page/index.rb', line 755

def prev_record
  Innodb::Stats.increment :page_record_cursor_prev_record

  slot = @page.directory_slot_for_record(@record)
  raise "Could not find slot for record" unless slot

  search_cursor = @page.record_cursor(@page.directory[slot - 1])
  raise "Could not position search cursor" unless search_cursor

  while (rec = search_cursor.record) && rec.offset != @record.offset
    next unless rec.next == @record.offset

    return if rec == @page.infimum

    return @record = rec
  end
end

#record ⇒ Object

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



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# File 'lib/innodb/page/index.rb', line 774

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

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