Class: Innodb::Xdes

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

Defined Under Namespace

Classes: Entry, PageStatus

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).

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

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

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

  # 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).
  4 => :fseg,
}.freeze

Instance Attribute Summary collapse

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 64

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

Instance Attribute Details

#xdes ⇒ Object (readonly)

Returns the value of attribute xdes.



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# File 'lib/innodb/xdes.rb', line 51

def xdes
  @xdes
end

Instance Method Details

#==(other) ⇒ Object

Compare one Innodb::Xdes to another.



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# File 'lib/innodb/xdes.rb', line 164

def ==(other)
  this.page == other.this.page && this.offset == other.this.offset
end

#allocated_to_fseg? ⇒ Boolean

Return whether this XDES entry is allocated to an fseg (the whole extent then belongs to the fseg).

Returns:

  • (Boolean) 


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# File 'lib/innodb/xdes.rb', line 99

def allocated_to_fseg?
  fseg_id != 0
end

#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 118

def each_page_status
  return enum_for(:each_page_status) unless block_given?

  bitmap.each_byte.with_index do |byte, byte_index|
    (0..3).each do |page_offset|
      page_number = start_page + (byte_index * 4) + page_offset
      page_bits = ((byte >> (page_offset * BITS_PER_PAGE)) & BITMAP_BV_ALL)
      page_status = PageStatus.new(
        free: (page_bits & BITMAP_BV_FREE != 0),
        clean: (page_bits & BITMAP_BV_CLEAN != 0)
      )
      yield page_number, 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 137

def free_pages
  each_page_status.inject(0) do |sum, (_page_number, page_status)|
    sum += 1 if page_status.free
    sum
  end
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 159

def next_address
  list.next
end

#page_status(page_number) ⇒ Object

Return the status for a given page. This is relatively inefficient as implemented and could be done better.



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# File 'lib/innodb/xdes.rb', line 105

def page_status(page_number)
  page_status_array = each_page_status.to_a
  page_status_array[page_number - start_page][1]
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 152

def prev_address
  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 80

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)
  cursor.name("xdes[#{extent_number}]") do |c|
    Entry.new(
      offset: c.position,
      start_page: start_page,
      end_page: start_page + page.space.pages_per_extent - 1,
      fseg_id: c.name("fseg_id") { c.read_uint64 },
      this: Innodb::Page::Address.new(page: page.offset, offset: c.position),
      list: c.name("list") { Innodb::List.get_node(c) },
      state: c.name("state") { STATES[c.read_uint32] },
      bitmap: c.name("bitmap") { c.read_bytes(size_bitmap) }
    )
  end
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 70

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 75

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 145

def used_pages
  @page.space.pages_per_extent - free_pages
end