8. A computer-readable storage medium having computer-executable instructions stored thereon which, when executed by a computer system, cause the computer system to perform a method comprising: traversing an iterator through at least a portion of at least one postings list in response to at least one search request, wherein the iterator includes fixed state information that remains constant over a life of the iterator, and dynamic state information that is updated over the life of the iterator, wherein the iterator includes a storage structure associated with the iterator for storing a representation of the dynamic state information, wherein a stack structure includes a pima it of entries for storing the representation of the dynamic state information in one of the entries and for storing at least a further representation of a further instance of the dynamic state information in a further one of the entries, wherein the storage structure further includes a representation of at least one checkpoint, and wherein the checkpoint represents at least one instance of the dynamic state information at a particular point during the iterator traversing through at least the portion of the postings list while performing a search; updating at least one instance of the dynamic state information as the iterator traverses through at least the portion of the postings list while performing the search; and evaluating whether to restore the iterator to a previous state represented by the dynamic state information represented by the checkpoint.
8. A computer-readable storage medium having computer-executable instructions stored thereon which, when executed by a computer system, cause the computer system to perform a method comprising: traversing an iterator through at least a portion of at least one postings list in response to at least one search request, wherein the iterator includes fixed state information that remains constant over a life of the iterator, and dynamic state information that is updated over the life of the iterator, wherein the iterator includes a storage structure associated with the iterator for storing a representation of the dynamic state information, wherein a stack structure includes a pima it of entries for storing the representation of the dynamic state information in one of the entries and for storing at least a further representation of a further instance of the dynamic state information in a further one of the entries, wherein the storage structure further includes a representation of at least one checkpoint, and wherein the checkpoint represents at least one instance of the dynamic state information at a particular point during the iterator traversing through at least the portion of the postings list while performing a search; updating at least one instance of the dynamic state information as the iterator traverses through at least the portion of the postings list while performing the search; and evaluating whether to restore the iterator to a previous state represented by the dynamic state information represented by the checkpoint. 11. The storage medium of claim 8 , further comprising instructions for evaluating whether the iterator is associated with at least one child iterator.