InnoDB Storage Engine Introduction-(5) InnoDB logical storage structure

If you create a table with no defined primary key displayed, MySQL creates the primary key as follows:

• First, determine if there is a non-empty unique index in the table, and if so, the column is the primary key.
• If the above conditions are not met, the storage engine automatically creates a 6-byte-size pointer.

When there are multiple, non-null, unique indexes in a table, the first non-null unique index defined when the table is built is selected. Note that the order in which the indexes are defined is not the order in which the columns are created.

• Tablespace tablespace (IBD file)
• Segment Segment (an index of 2 segments)
• Extent (1MB)
• Page (16KB)
• Row
• Field

Table Space

InnoDB Storage Engine Introduction-(5) InnoDB logical storage structure