38. The computer program product of claim 37 , wherein the tag assignment module further includes instructions for detecting satisfaction of a merge condition, and for, when the merge condition is satisfied, performing a merge operation, the merge operation including merging a layered plurality of sorted maps produced by previous flushing operations, the merge operation further including producing a merged map relating globally unique identifiers to document identification tags assigned to documents.
37. The computer program product of claim 29 , wherein the tag assignment module further includes instructions for detecting satisfaction of a flush condition and for, when the flush condition is satisfied, executing a flush operation, including building a sorted map, the sorted map relating globally unique identifiers to document identification tags assigned to documents since a prior flush operation.