Class: Innodb::Xdes

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

Overview

An InnoDB “extent descriptor entry” or “XDES”. These structures are used in the XDES entry array contained in FSP_HDR and XDES pages.

Note the distinction between XDES entries and XDES pages.

Constant Summary collapse

BITS_PER_PAGE =

Number of bits per page in the XDES entry bitmap field. Currently XDES entries store two bits per page, with the following meanings:

  • 1 = free (the page is free, or not in use)

  • 2 = clean (currently unused, always 1 when initialized)

2
BITMAP_BV_FREE =

The bit value for a free page.

1
BITMAP_BV_CLEAN =

The bit value for a clean page (currently unused in InnoDB).

2
BITMAP_BV_ALL =

The bitwise-OR of all bitmap bit values.

(BITMAP_BV_FREE | BITMAP_BV_CLEAN)
STATES =

The values used in the :state field indicating what the extent is used for (or what list it is on).

{
  1 => :free,       # The extent is completely empty and unused, and should
                    # be present on the filespace's FREE list.

  2 => :free_frag,  # Some pages of the extent are used individually, and
                    # the extent should be present on the filespace's
                    # FREE_FRAG list.

  3 => :full_frag,  # All pages of the extent are used individually, and
                    # the extent should be present on the filespace's
                    # FULL_FRAG list.

  4 => :fseg,       # The extent is wholly allocated to a file segment.
                    # Additional information about the state of this extent
                    # can be derived from the its presence on particular
                    # file segment lists (FULL, NOT_FULL, or FREE).
}

Instance Method Summary collapse

Constructor Details

#initialize(page, cursor) ⇒ Xdes

Returns a new instance of Xdes.



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# File 'lib/innodb/xdes.rb', line 42

def initialize(page, cursor)
  @page = page
  @xdes = read_xdes_entry(page, cursor)
end

Instance Method Details

#each_page_status ⇒ Object

Iterate through all pages represented by this extent descriptor, yielding a page status hash for each page, containing the following fields:

:page   The page number.
:free   Boolean indicating whether the page is free.
:clean  Boolean indicating whether the page is clean (currently
        this bit is unused by InnoDB, and always set true).



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# File 'lib/innodb/xdes.rb', line 84

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

  bitmap = xdes[:bitmap].enum_for(:each_byte)

  bitmap.each_with_index do |byte, byte_index|
    (0..3).each_with_index do |page, page_index|
      page_number = xdes[:start_page] + (byte_index * 4) + page_index
      page_bits = ((byte >> (page * BITS_PER_PAGE)) & BITMAP_BV_ALL)
      page_status = {
        :page   => page_number,
        :free   => (page_bits & BITMAP_BV_FREE  != 0),
        :clean  => (page_bits & BITMAP_BV_CLEAN != 0),
      }
      yield page_status
    end
  end

  nil
end

#free_pages ⇒ Object

Return the count of free pages (free bit is true) on this extent.



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# File 'lib/innodb/xdes.rb', line 108

def free_pages
  each_page_status.inject(0) { |sum, p| sum += 1 if p[:free]; sum }
end

#next_address ⇒ Object

Return the address of the next list pointer from the list node contained within the XDES entry. This is used by Innodb::List::Xdes to iterate through XDES entries in a list.



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# File 'lib/innodb/xdes.rb', line 127

def next_address
  xdes[:list][:next]
end

#prev_address ⇒ Object

Return the address of the previous list pointer from the list node contained within the XDES entry. This is used by Innodb::List::Xdes to iterate through XDES entries in a list.



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# File 'lib/innodb/xdes.rb', line 120

def prev_address
  xdes[:list][:prev]
end

#read_xdes_entry(page, cursor) ⇒ Object

Read an XDES entry from a cursor.



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# File 'lib/innodb/xdes.rb', line 58

def read_xdes_entry(page, cursor)
  extent_number = (cursor.position - page.pos_xdes_array) / size_entry
  start_page = page.offset + (extent_number * page.space.pages_per_extent)
  {
    :start_page => start_page,
    :fseg_id    => cursor.get_uint64,
    :this       => {:page => page.offset, :offset => cursor.position},
    :list       => Innodb::List.get_node(cursor),
    :state      => STATES[cursor.get_uint32],
    :bitmap     => cursor.get_bytes(size_bitmap),
  }
end

#size_bitmap ⇒ Object

Size (in bytes) of the bitmap field in the XDES entry.



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# File 'lib/innodb/xdes.rb', line 48

def size_bitmap
  (@page.space.pages_per_extent * BITS_PER_PAGE) / 8
end

#size_entry ⇒ Object

Size (in bytes) of the an XDES entry.



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# File 'lib/innodb/xdes.rb', line 53

def size_entry
  8 + Innodb::List::NODE_SIZE + 4 + size_bitmap
end

#used_pages ⇒ Object

Return the count of used pages (free bit is false) on this extent.



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# File 'lib/innodb/xdes.rb', line 113

def used_pages
  @page.space.pages_per_extent - free_pages
end

#xdes ⇒ Object

Return the stored extent descriptor entry.



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# File 'lib/innodb/xdes.rb', line 72

def xdes
  @xdes
end