Class Innodb::Xdes
In: lib/innodb/xdes.rb
Parent: Object

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.

Methods

==   allocated_to_fseg?   bitmap   each_page_status   end_page   free_pages   fseg_id   list   new   next_address   offset   page_status   prev_address   read_xdes_entry   size_bitmap   size_entry   start_page   state   this   used_pages   xdes  

Constants

BITS_PER_PAGE = 2   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)
BITMAP_BV_FREE = 1   The bit value for a free page.
BITMAP_BV_CLEAN = 2   The bit value for a clean page (currently unused in InnoDB).
BITMAP_BV_ALL = (BITMAP_BV_FREE | BITMAP_BV_CLEAN)   The bitwise-OR of all bitmap bit values.
STATES = { 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). }   The values used in the +:state+ field indicating what the extent is used for (or what list it is on).

Public Class methods

Public Instance methods

==(other)

Compare one Innodb::Xdes to another.

allocated_to_fseg?()

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

each_page_status() {|page_number, page_status| ...}

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).
free_pages()

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

next_address()

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.

page_status(page_number)

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

prev_address()

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.

read_xdes_entry(page, cursor)

Read an XDES entry from a cursor.

size_bitmap()

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

size_entry()

Size (in bytes) of the an XDES entry.

used_pages()

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

xdes()

Return the stored extent descriptor entry.

[Validate]