Index-level derived statistics

The derived statistics in the index-level section are based on the “CR count” values shown in “Index statistics”.

**Table 6-5: Cluster ratios for a nonclustered index**
Row label	Information provided
Data page cluster ratio	The fraction of row accesses that do not require an additional extent I/O because of storage fragmentation, while accessing rows in order by this index using large I/O. It is a measure of the sequencing of data pages on extents.
Index page cluster ratio	The fraction of index leaf page accesses via the page chain that do not require extra extent I/O. It is a measure of the sequencing of index pages on extents.
Data row cluster ratio	The fraction of data page accesses that do not require an extra I/O when accessing data rows in order by this index. It is a measure of the sequencing of rows on data pages.
Space utilization	The ratio of the minimum space usage for the leaf level of this index, and the current space usage.
Large I/O efficiency	Estimates the number of useful pages brought in by each large I/O.