Class: Innodb::Page::Index

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

Overview

A specialized class for handling INDEX pages, which contain a portion of the data from exactly one B+tree. These are typically the most common type of page in any database.

The basic structure of an INDEX page is: FIL header, INDEX header, FSEG header, fixed-width system records (infimum and supremum), user records (the actual data) which grow ascending by offset, free space, the page directory which grows descending by offset, and the FIL trailer.

Defined Under Namespace

Classes: RecordCursor

Constant Summary collapse

PAGE_DIRECTION =

Page direction values possible in the page_header’s :direction field.

{
  1 => :left,           # Inserts have been in descending order.
  2 => :right,          # Inserts have been in ascending order.
  3 => :same_rec,       # Unused by InnoDB.
  4 => :same_page,      # Unused by InnoDB.
  5 => :no_direction,   # Inserts have been in random order.
}
RECORD_BITS_SIZE =

The size (in bytes) of the bit-packed fields in each record header.

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RECORD_NEXT_SIZE =

The size (in bytes) of the “next” pointer in each record header.

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PAGE_DIR_SLOT_SIZE =

The size (in bytes) of the record pointers in each page directory slot.

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PAGE_DIR_SLOT_MIN_N_OWNED =

The minimum number of records “owned” by each record with an entry in the page directory.

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PAGE_DIR_SLOT_MAX_N_OWNED =

The maximum number of records “owned” by each record with an entry in the page directory.

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RECORD_TYPES =

Record types used in the :type field of the record header.

{
  0 => :conventional,   # A normal user record in a leaf page.
  1 => :node_pointer,   # A node pointer in a non-leaf page.
  2 => :infimum,        # The system "infimum" record.
  3 => :supremum,       # The system "supremum" record.
}
RECORD_INFO_MIN_REC_FLAG =

This record is the minimum record at this level of the B-tree.

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RECORD_INFO_DELETED_FLAG =

This record has been marked as deleted.

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Constants inherited from Innodb::Page

PAGE_TYPE, SPECIALIZED_CLASSES

Instance Attribute Summary collapse

Attributes inherited from Innodb::Page

#space

Instance Method Summary collapse

Methods inherited from Innodb::Page

#cursor, #data, #fil_header, #initialize, #inspect, #lsn, maybe_undefined, #next, #offset, parse, #pos_fil_header, #pos_fil_trailer, #prev, #size, #size_fil_header, #size_fil_trailer, #type

Constructor Details

This class inherits a constructor from Innodb::Page

Instance Attribute Details

#record_describer ⇒ Object

Returns the value of attribute record_describer.



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# File 'lib/innodb/page/index.rb', line 12

def record_describer
  @record_describer
end

Instance Method Details

#directory ⇒ Object

Return an array of row offsets for all entries in the page directory.



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# File 'lib/innodb/page/index.rb', line 483

def directory
  return @directory if @directory

  @directory = []
  c = cursor(pos_directory).backward
  directory_slots.times do
    @directory.push c.get_uint16
  end

  @directory
end

#directory_slots ⇒ Object

The number of directory slots in use.



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# File 'lib/innodb/page/index.rb', line 83

def directory_slots
  page_header[:n_dir_slots]
end

#directory_space ⇒ Object

The amount of space consumed by the page directory.



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# File 'lib/innodb/page/index.rb', line 88

def directory_space
  directory_slots * PAGE_DIR_SLOT_SIZE
end

#dump ⇒ Object

Dump the contents of a page for debugging purposes.



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# File 'lib/innodb/page/index.rb', line 496

def dump
  super

  puts "page header:"
  pp page_header
  puts

  puts "fseg header:"
  pp fseg_header
  puts

  puts "sizes:"
  puts "  %-15s%5i" % [ "header",     header_space ]
  puts "  %-15s%5i" % [ "trailer",    trailer_space ]
  puts "  %-15s%5i" % [ "directory",  directory_space ]
  puts "  %-15s%5i" % [ "free",       free_space ]
  puts "  %-15s%5i" % [ "used",       used_space ]
  puts "  %-15s%5i" % [ "record",     record_space ]
  puts "  %-15s%5.2f" % [
    "per record",
    (page_header[:n_recs] > 0) ? (record_space / page_header[:n_recs]) : 0
  ]
  puts

  puts "system records:"
  pp infimum
  pp supremum
  puts

  puts "page directory:"
  pp directory
  puts

  puts "records:"
  each_record do |rec|
    pp rec
  end
  puts
end

#each_child_page ⇒ Object

Iterate through all child pages of a node (non-leaf) page, which are stored as records with the child page number as the last field in the record.



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# File 'lib/innodb/page/index.rb', line 468

def each_child_page
  return nil if level == 0

  unless block_given?
    return enum_for(:each_child_page)
  end

  each_record do |rec|
    yield rec[:child_page_number], rec[:key]
  end

  nil
end

#each_record ⇒ Object

Iterate through all records.



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# File 'lib/innodb/page/index.rb', line 451

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

  c = record_cursor(infimum[:next])

  while rec = c.record
    yield rec
  end

  nil
end

#first_record ⇒ Object

Return the first record on this page.



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# File 'lib/innodb/page/index.rb', line 445

def first_record
  first = record(infimum[:next])
  first if first != supremum
end

#free_space ⇒ Object

Return the amount of free space in the page.



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# File 'lib/innodb/page/index.rb', line 98

def free_space
  page_header[:garbage] +
    (size - size_fil_trailer - directory_space - page_header[:heap_top])
end

#fseg_header ⇒ Object

Return the “fseg” header.



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# File 'lib/innodb/page/index.rb', line 166

def fseg_header
  c = cursor(pos_fseg_header)
  @fseg_header ||= {
    :leaf     => Innodb::FsegEntry.get_inode(@space, c),
    :internal => Innodb::FsegEntry.get_inode(@space, c),
  }
end

#header_space ⇒ Object

The amount of space consumed by the page header.



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# File 'lib/innodb/page/index.rb', line 76

def header_space
  # The end of the supremum system record is the beginning of the space
  # available for user records.
  pos_user_records
end

#infimum ⇒ Object

Return the infimum record on a page.



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# File 'lib/innodb/page/index.rb', line 318

def infimum
  @infimum ||= system_record(pos_infimum)
end

#level ⇒ Object

A helper function to return the page level from the “page” header, for easier access.



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# File 'lib/innodb/page/index.rb', line 150

def level
  page_header && page_header[:level]
end

#make_record_description ⇒ Object

Return a set of field objects that describe the record.



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# File 'lib/innodb/page/index.rb', line 328

def make_record_description
  description = record_describer.cursor_sendable_description(self)

  fields = []

  (description[:key] + description[:row]).each_with_index do |d, p|
    fields << Innodb::Field.new(p, *d)
  end

  n = description[:key].size

  description[:key] = fields.slice(0 .. n-1)
  description[:row] = fields.slice(n ..  -1)

  return description
end

#page_header ⇒ Object

Return the “index” header.



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# File 'lib/innodb/page/index.rb', line 129

def page_header
  c = cursor(pos_index_header)
  @page_header ||= {
    :n_dir_slots  => c.get_uint16,
    :heap_top     => c.get_uint16,
    :n_heap       => ((n_heap = c.get_uint16) & (2**15-1)),
    :free         => c.get_uint16,
    :garbage      => c.get_uint16,
    :last_insert  => c.get_uint16,
    :direction    => PAGE_DIRECTION[c.get_uint16],
    :n_direction  => c.get_uint16,
    :n_recs       => c.get_uint16,
    :max_trx_id   => c.get_uint64,
    :level        => c.get_uint16,
    :index_id     => c.get_uint64,
    :format       => (n_heap & 1<<15) == 0 ? :redundant : :compact,
  }
end

#pos_directory ⇒ Object

The position of the page directory, which starts at the “fil” trailer and grows backwards from there.



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# File 'lib/innodb/page/index.rb', line 71

def pos_directory
  pos_fil_trailer
end

#pos_fseg_header ⇒ Object

Return the byte offset of the start of the “fseg” header, which immediately follows the “index” header.



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# File 'lib/innodb/page/index.rb', line 27

def pos_fseg_header
  pos_index_header + size_index_header
end

#pos_index_header ⇒ Object

Return the byte offset of the start of the “index” page header, which immediately follows the “fil” header.



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# File 'lib/innodb/page/index.rb', line 16

def pos_index_header
  pos_fil_header + size_fil_header
end

#pos_infimum ⇒ Object

Return the byte offset of the start of the “origin” of the infimum record, which is always the first record in the singly-linked record chain on any page, and represents a record with a “lower value than any possible user record”. The infimum record immediately follows the page header.



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# File 'lib/innodb/page/index.rb', line 51

def pos_infimum
  pos_records + size_record_header + size_record_undefined
end

#pos_records ⇒ Object

Return the byte offset of the start of records within the page (the position immediately after the page header).



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# File 'lib/innodb/page/index.rb', line 38

def pos_records
  size_fil_header + size_index_header + size_fseg_header
end

#pos_supremum ⇒ Object

Return the byte offset of the start of the “origin” of the supremum record, which is always the last record in the singly-linked record chain on any page, and represents a record with a “higher value than any possible user record”. The supremum record immediately follows the infimum record.



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# File 'lib/innodb/page/index.rb', line 59

def pos_supremum
  pos_infimum + size_record_header + size_record_undefined + size_mum_record
end

#pos_user_records ⇒ Object

Return the byte offset of the start of the user records in a page, which immediately follows the supremum record.



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# File 'lib/innodb/page/index.rb', line 65

def pos_user_records
  pos_supremum + size_mum_record
end

#record(offset) ⇒ Object

Parse and return a record at a given offset.



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# File 'lib/innodb/page/index.rb', line 353

def record(offset)
  return nil unless offset
  return infimum  if offset == pos_infimum
  return supremum if offset == pos_supremum

  c = cursor(offset).forward

  # There is a header preceding the row itself, so back up and read it.
  header = record_header(offset)

  this_record = {
    :format => page_header[:format],
    :offset => offset,
    :header => header,
    :next => header[:next] == 0 ? nil : (offset + header[:next]),
  }

  if record_format
    this_record[:type] = record_format[:type]

    # Read the key fields present in all types of pages.
    this_record[:key] = []
    record_format[:key].each do |f|
      this_record[:key].push f.read(this_record, c)
    end

    # If this is a leaf page of the clustered index, read InnoDB's internal
    # fields, a transaction ID and roll pointer.
    if level == 0 && record_format[:type] == :clustered
      this_record[:transaction_id] = c.get_hex(6)
      first_byte = c.get_uint8
      this_record[:roll_pointer]   = {
        :is_insert  => (first_byte & 0x80) == 0x80,
        :rseg_id    => first_byte & 0x7f,
        :undo_log => {
          :page       => c.get_uint32,
          :offset     => c.get_uint16,
        }
      }
    end

    # If this is a leaf page of the clustered index, or any page of a
    # secondary index, read the non-key fields.
    if (level == 0 && record_format[:type] == :clustered) ||
      (record_format[:type] == :secondary)
      # Read the non-key fields.
      this_record[:row] = []
      record_format[:row].each do |f|
        this_record[:row].push f.read(this_record, c)
      end
    end

    # If this is a node (non-leaf) page, it will have a child page number
    # (or "node pointer") stored as the last field.
    if level > 0
      # Read the node pointer in a node (non-leaf) page.
      this_record[:child_page_number] = c.get_uint32
    end
  end

  this_record
end

#record_bytes ⇒ Object

Return the actual bytes of the portion of the page which is used to store user records (eliminate the headers and trailer from the page).



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# File 'lib/innodb/page/index.rb', line 115

def record_bytes
  data(pos_user_records, page_header[:heap_top] - pos_user_records)
end

#record_cursor(offset) ⇒ Object

Return a RecordCursor starting at offset.



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# File 'lib/innodb/page/index.rb', line 440

def record_cursor(offset)
  RecordCursor.new(self, offset)
end

#record_format ⇒ Object

Return (and cache) the record format provided by an external class.



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# File 'lib/innodb/page/index.rb', line 346

def record_format
  if record_describer
    @record_format ||= make_record_description()
  end
end

#record_header(offset) ⇒ Object

Return the header from a record.



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# File 'lib/innodb/page/index.rb', line 227

def record_header(offset)
  c = cursor(offset).backward
  case page_header[:format]
  when :compact
    header = {}
    header[:next] = c.get_sint16
    bits1 = c.get_uint16
    header[:type] = RECORD_TYPES[bits1 & 0x07]
    header[:order] = (bits1 & 0xf8) >> 3
    bits2 = c.get_uint8
    header[:n_owned] = bits2 & 0x0f
    info = (bits2 & 0xf0) >> 4
    header[:min_rec] = (info & RECORD_INFO_MIN_REC_FLAG) != 0
    header[:deleted] = (info & RECORD_INFO_DELETED_FLAG) != 0
    case header[:type]
    when :conventional, :node_pointer
      # The variable-length part of the record header contains a
      # bit vector indicating NULL fields and the length of each
      # non-NULL variable-length field.
      if record_format
        header[:null_bitmap] = nbmap = record_null_bitmap(c)
        header[:variable_length] = record_variable_length(c, nbmap)
      end
    end
    header
  when :redundant
    raise "Not implemented"
  end
end

#record_null_bitmap(cursor) ⇒ Object

Return an array indicating which fields are null.



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# File 'lib/innodb/page/index.rb', line 258

def record_null_bitmap(cursor)
  fields = (record_format[:key] + record_format[:row])

  # The number of bits in the bitmap is the number of nullable fields.
  size = fields.count do |f| f.nullable end

  # There is no bitmap if there are no nullable fields.
  return nil unless size > 0

  # To simplify later checks, expand bitmap to one for each field.
  bitmap = Array.new(fields.size, false)

  null_bit_array = cursor.get_bit_array(size).reverse!

  # For every nullable field, set whether the field is actually null.
  fields.each do |f|
    bitmap[f.position] = f.nullable ? (null_bit_array.shift == 1) : false
  end

  return bitmap
end

#record_space ⇒ Object

Return the amount of space occupied by records in the page.



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# File 'lib/innodb/page/index.rb', line 109

def record_space
  used_space - header_space - directory_space - trailer_space
end

#record_variable_length(cursor, null_bitmap) ⇒ Object

Return an array containing the length of each variable-length field.



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# File 'lib/innodb/page/index.rb', line 281

def record_variable_length(cursor, null_bitmap)
  fields = (record_format[:key] + record_format[:row])

  len_array = Array.new(fields.size, 0)

  # For each non-NULL variable-length field, the record header contains
  # the length in one or two bytes.
  fields.each do |f|
    next if f.fixed_len > 0 or null_bitmap[f.position]

    len = cursor.get_uint8

    # Two bytes are used only if the length exceeds 127 bytes and the
    # maximum length exceeds 255 bytes.
    if len > 127 and f.variable_len > 255
      len = ((len & 0x3f) << 8) + cursor.get_uint8
    end

    len_array[f.position] = len
  end

  return len_array
end

#records ⇒ Object

A helper function to return the number of records.



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# File 'lib/innodb/page/index.rb', line 155

def records
  page_header && page_header[:n_recs]
end

#root? ⇒ Boolean

A helper function to identify root index pages; they must be the only pages at their level.

Returns:

  • (Boolean) 


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# File 'lib/innodb/page/index.rb', line 161

def root?
  self.prev.nil? && self.next.nil?
end

#size_fseg_header ⇒ Object

The size of the “fseg” header.



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# File 'lib/innodb/page/index.rb', line 32

def size_fseg_header
  2 * Innodb::FsegEntry::SIZE
end

#size_index_header ⇒ Object

The size of the “index” header.



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

def size_index_header
  36
end

#size_mum_record ⇒ Object

The size of the data from the supremum or infimum records.



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# File 'lib/innodb/page/index.rb', line 43

def size_mum_record
  8
end

#size_record_header ⇒ Object

Return the size of the header for each record.



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# File 'lib/innodb/page/index.rb', line 192

def size_record_header
  case page_header[:format]
  when :compact
    RECORD_BITS_SIZE + RECORD_NEXT_SIZE
  when :redundant
    RECORD_BITS_SIZE + RECORD_NEXT_SIZE + 1
  end
end

#size_record_undefined ⇒ Object

Return the size of a field in the record header for which no description could be found (but must be skipped anyway).



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# File 'lib/innodb/page/index.rb', line 203

def size_record_undefined
  case page_header[:format]
  when :compact
    0
  when :redundant
    1
  end
end

#supremum ⇒ Object

Return the supremum record on a page.



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# File 'lib/innodb/page/index.rb', line 323

def supremum
  @supremum ||= system_record(pos_supremum)
end

#system_record(offset) ⇒ Object

Parse and return simple fixed-format system records, such as InnoDB’s internal infimum and supremum records.



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# File 'lib/innodb/page/index.rb', line 307

def system_record(offset)
  header = record_header(offset)
  {
    :offset => offset,
    :header => header,
    :next => offset + header[:next],
    :data => cursor(offset).get_bytes(size_mum_record),
  }
end

#trailer_space ⇒ Object

The amount of space consumed by the trailers in the page.



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# File 'lib/innodb/page/index.rb', line 93

def trailer_space
  size_fil_trailer
end

#used_space ⇒ Object

Return the amount of used space in the page.



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# File 'lib/innodb/page/index.rb', line 104

def used_space
  size - free_space
end