This section reports index maintenance activity caused by page splits in allpages-locked tables with clustered indexes. These splits require updating the nonclustered indexes for all of the rows that move to the new data page.
RID Upd from Clust Split – reports the total number of page splits that required maintenance of a nonclustered index.
# of NC Ndx Maint – reports the number of nonclustered rows that required maintenance as a result of row ID update operations.
Avg NC Ndx Maint/Op – reports the average number of nonclustered indexes entries that were updated for each page split.