What are index-organized tables (IOT)?

What are index-organized tables (IOT)?

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Index-organized tables are used for storing table data in sorted order. The rows in index-organized tables are stored in a primary key sorted order of the B-Tree index structure. This is unlike the heap organization method that is generally adopted by a simple table structure where the rows are stored in the order of their insertion. In an index-organized table structure, the index actually stores the row data instead of containing a pointer to the location of the row data. This mechanism enhances the performance of queries by retrieving the rows faster than the conventional row storage mechanisms such as heap organization method. Data storage in index-organized tables is done in a typical inverted-tree structure with the leaves storing the actual data. The primary advantage of using index-organized tables is that the rows dynamically adjust themselves in case of row insertions, to maintain the sorted order. In this way, the performance enhancement by using IOT is retained.

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