Nonclustered Index Spool Showplan Operator
The Index Spool physical operator contains a SEEK:() predicate in the Argument column. The Index Spool operator scans its input rows, placing a copy of each row in a hidden spool file (stored in the tempdb database and existing only for the lifetime of the query), and builds a nonclustered index on the rows. This allows you to use the seeking capability of indexes to output only those rows that satisfy the SEEK:() predicate.
If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input.
Graphical execution plan icon