MySQL Internals Manual  /  ...  /  High-Altitude Picture

22.1.1 High-Altitude Picture

The chart below shows the three parts of a physical record.

Name Size
Field Start Offsets (F*1) or (F*2) bytes
Extra Bytes 6 bytes
Field Contents depends on content

Legend: The letter 'F' stands for 'Number Of Fields'.

The meaning of the parts is as follows:

  • The FIELD START OFFSETS is a list of numbers containing the information "where a field starts".

  • The EXTRA BYTES is a fixed-size header.

  • The FIELD CONTENTS contains the actual data.

An Important Note About The Word "Origin"

The "Origin" or "Zero Point" of a record is the first byte of the Field Contents --- not the first byte of the Field Start Offsets. If there is a pointer to a record, that pointer is pointing to the Origin. Therefore the first two parts of the record are addressed by subtracting from the pointer, and only the third part is addressed by adding to the pointer.