Physical Index Structures

Index pages have almost the same structure as data pages except that they store index records instead of data records. As with all other types of pages in SQL Server, index pages use a fixed size of 8 KB, or 8,192 bytes. Index pages also have a 96-byte header, and there is an offset array at the end of the page with 2 bytes for each row to indicate the offset of that row on the page. A nonclustered index can have all three allocation units associated with it: IN_ROW_DATA, ROW_OVERFLOW_DATA, and LOB_DATA. Each index has a row in the sys.indexes catalog view, with an index_id value of either 1 (for a clustered index) or a number between 2 and 250 or between 256 and 1005 (indicating a nonclustered index). Remember that SQL ...

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