11. The system of claim 10 , wherein the term assigned to the second leaf node is a first term and wherein the instructions further include instructions that, when executed, cause the first leaf node to: receive an updated term-sharded posting list portion for a second term from a third leaf node, the second term being assigned to the first leaf node; receive an updated term-sharded posting list portion for the second term from a fourth leaf node; merge the updated term-sharded posting list portion from the third leaf node with the updated term-sharded posting list portion from the fourth leaf node to generate a new term-sharded posting list for the second term; and and use the new term-sharded posting list for the second term in responding to queries.
10. A system comprising: distributed computing devices represented as leaf nodes and a root node; and an index of documents, the index being distributed across the leaf nodes, the documents being assigned to respective leaf nodes, and wherein a first leaf node includes: memory storing document-sharded posting lists for some or all terms associated with documents in a first set of documents that are assigned to the first leaf node, and memory storing term-sharded posting lists for terms assigned to the first leaf node without regard to leaf node assignments for documents identified in the term-sharded posting lists, wherein the first leaf node includes: at least one processor, memory storing instructions that, when executed by the at least one processor, cause the first leaf node to: receive an update for documents assigned to the first leaf node, determine that the update affects the at least one document-sharded posting list and, responsive to the determining, generate an updated document-sharded posting list for the at least one document-sharded posting list, and determine that the update affects a term-sharded posting list for a term assigned to a second leaf node, the term being associated with at least one document in a second set of documents that are assigned to the first leaf and not in the first set of documents and, responsive to the determining: generate change information for the documents associated with the term, generate an updated term-sharded posting list for the term, and provide the change information and the updated term-sharded posting list to the second leaf node.