Class: Innodb::Page::FspHdrXdes

Inherits:
Innodb::Page show all
Defined in:
lib/innodb/page/fsp_hdr_xdes.rb

Overview

A specialized class for FSP_HDR (filespace header) and XDES (extent descriptor) page types. Each tablespace always has an FSP_HDR page as its first page (page 0), and has repeating XDES pages every 16,384 pages after that (page 16384, 32768, ...). The FSP_HDR and XDES page structure is completely identical, with the exception that the FSP header structure is zero-filled on XDES pages, but populated on FSP_HDR pages.

The basic structure of FSP_HDR and XDES pages is: FIL header, FSP header, an array of 256 XDES entries, empty (unused) space, and FIL trailer.

Constant Summary collapse

FLAGS_PAGE_SIZE_ADJUST =

A value added to the adjusted exponent stored in the page size field of the flags in the FSP header.

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Constants inherited from Innodb::Page

PAGE_TYPE, SPECIALIZED_CLASSES

Instance Attribute Summary

Attributes inherited from Innodb::Page

#space

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Innodb::Page

#calculate_checksum, #checksum, #corrupt?, #cursor, #data, #fil_header, handle, #initialize, #inspect, #lsn, maybe_undefined, #next, #offset, parse, #pos_fil_header, #pos_fil_trailer, #pos_page_body, #prev, #size, #size_fil_header, #size_fil_trailer, #type

Constructor Details

This class inherits a constructor from Innodb::Page

Class Method Details

.decode_flags(flags) ⇒ Object

Decode the "flags" field in the FSP header, returning a hash of useful decoded flags. Unfortunately, InnoDB has a fairly weird and broken implementation of these flags. The flags are:

Offset Size Description 0 1 Page Format (redundant, compact). This is unfortunately coerced to 0 if it is "compact" and no other flags are set, making it useless to innodb_ruby. 1 4 Compressed Page Size (zip_size). This is stored as a power of 2, minus 9. Since 0 is reserved to mean "not compressed", the minimum value is 1, thus making the smallest page size 1024 (2 ** (9 + 1)). 5 1 Table Format (Antelope, Barracuda). This was supposed to reserve 6 bits, but due to a bug in InnoDB only actually reserved 1 bit.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 41

def self.decode_flags(flags)
  # The page size for compressed pages is stored at bit offset 1 and consumes
  # 4 bits. Value 0 means the page is not compressed.
  page_size = read_bits_at_offset(flags, 4, 1)
  {
    :compressed => page_size == 0 ? false : true,
    :page_size => page_size == 0 ?
      Innodb::Space::DEFAULT_PAGE_SIZE :
      (1 << (FLAGS_PAGE_SIZE_ADJUST + page_size)),
    :value => flags,
  }
end

.read_bits_at_offset(data, bits, offset) ⇒ Object

Read a given number of bits from an integer at a specific bit offset. The value returned is 0-based so does not need further shifting or adjustment.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 21

def self.read_bits_at_offset(data, bits, offset)
  ((data & (((1 << bits) - 1) << offset)) >> offset)
end

Instance Method Details

#dump ⇒ Object

Dump the contents of a page for debugging purposes.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 137

def dump
  super

  puts "fsp header:"
  pp fsp_header
  puts

  puts "xdes entries:"
  each_xdes do |xdes|
    pp xdes
  end
  puts
end

#each_list ⇒ Object

Iterate through all lists in the file space.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 110

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

  fsp_header.each do |key, value|
    yield key, value if value.is_a?(Innodb::List)
  end
end

#each_xdes ⇒ Object

Iterate through all XDES entries in order. This is useful for debugging, but each of these entries is actually a node in some other list. The state field in the XDES entry indicates which type of list it is present in, although not necessarily which list (e.g. :fseg).



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 124

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

  cursor(pos_xdes_array).name("xdes_array") do |c|
    entries_in_xdes_array.times do |n|
      yield Innodb::Xdes.new(self, c)
    end
  end
end

#entries_in_xdes_array ⇒ Object

The number of entries in the XDES array. Defined as page size divided by extent size.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 72

def entries_in_xdes_array
  size / space.pages_per_extent
end

#fsp_header ⇒ Object

Read the FSP (filespace) header, which contains a few counters and flags, as well as list base nodes for each list maintained in the filespace.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 78

def fsp_header
  @fsp_header ||= cursor(pos_fsp_header).name("fsp") do |c|
    {
      :space_id           => c.name("space_id") { c.get_uint32 },
      :unused             => c.name("unused") { c.get_uint32 },
      :size               => c.name("size") { c.get_uint32 },
      :free_limit         => c.name("free_limit") { c.get_uint32 },
      :flags              => c.name("flags") { 
        self.class.decode_flags(c.get_uint32)
      },
      :frag_n_used        => c.name("frag_n_used") { c.get_uint32 },
      :free               => c.name("list[free]") {
        Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c))
      },
      :free_frag          => c.name("list[free_frag]") {
        Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c))
      },
      :full_frag          => c.name("list[full_frag]") {
        Innodb::List::Xdes.new(@space, Innodb::List.get_base_node(c))
      },
      :first_unused_seg   => c.name("first_unused_seg") { c.get_uint64 },
      :full_inodes        => c.name("list[full_inodes]") {
        Innodb::List::Inode.new(@space, Innodb::List.get_base_node(c))
      },
      :free_inodes        => c.name("list[free_inodes]") {
        Innodb::List::Inode.new(@space, Innodb::List.get_base_node(c))
      },
    }
  end
end

#pos_fsp_header ⇒ Object

The FSP header immediately follows the FIL header.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 55

def pos_fsp_header
  pos_fil_header + size_fil_header
end

#pos_xdes_array ⇒ Object

The XDES entry array immediately follows the FSP header.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 66

def pos_xdes_array
  pos_fsp_header + size_fsp_header
end

#size_fsp_header ⇒ Object

The FSP header contains six 32-bit integers, one 64-bit integer, and 5 list base nodes.



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# File 'lib/innodb/page/fsp_hdr_xdes.rb', line 61

def size_fsp_header
  ((4 * 6) + (1 * 8) + (5 * Innodb::List::BASE_NODE_SIZE))
end