10. Choosing Storage Structures and Secondary Indexes : Heap Storage Structure
 
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Heap Storage Structure
In a heap structure, the table has no key--it is simply a heap of data. When you add a row, it is added to the end of the heap. This makes heap the fastest storage structure to use when you are initially loading tables or adding a large quantity of data.
However, when you want to retrieve a particular row from a heap table, you must search through every row in the table looking for rows that qualify. This makes heap relatively slow for retrieval if tables have more than a few pages. For more information, see the chapter “Maintaining Storage Structures.”
Note:  The heapsort structure is like heap, but with the rows sorted and duplicates removed (unless duplicates are allowed).