InnoDB Data Storage and Compression

InnoDB Data Storage and Compression
All user data in InnoDB tables is stored in pages comprising a B-tree index (the clustered index). In
some other database systems, this type of index is called an “index-organized table”. Each row in the
index node contains the values of the (user-specified or system-generated) primary key and all the
other columns of the table.
Secondary indexes in InnoDB tables are also B-trees, containing pairs of values: the index key and a
pointer to a row in the clustered index. The pointer is in fact the value of the primary key of the table,
which is used to access the clustered index if columns other than the index key and primary key are
required. Secondary index records must always fit on a single B-tree page.
The compression of B-tree nodes (of both clustered and secondary indexes) is handled differently from
compression of overflow pages used to store long VARCHAR, BLOB, or TEXT columns, as explained in
the following sections.
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