30. A system, comprising: one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations comprising: receiving a re-submitted query and a first time token from a client, wherein the first time token is data that identifies a most-recent time that any resource identified by any of the real-time search results presented by the client was undated; identifying real-time search results that are responsive to the re-submitted query and are more recent than the time identified by the first time token, wherein an identified real-time search result is more recent than the most recent time identified by the first time token received from the client when a resource identified by the identified real-time search received from the client; and sending the identified real-time search results and a second time token to the client, wherein the second time token is data the identifies a most-recent time that any resource identified by any of the identified real-time search results was updated.
30. A system, comprising: one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations comprising: receiving a re-submitted query and a first time token from a client, wherein the first time token is data that identifies a most-recent time that any resource identified by any of the real-time search results presented by the client was undated; identifying real-time search results that are responsive to the re-submitted query and are more recent than the time identified by the first time token, wherein an identified real-time search result is more recent than the most recent time identified by the first time token received from the client when a resource identified by the identified real-time search received from the client; and sending the identified real-time search results and a second time token to the client, wherein the second time token is data the identifies a most-recent time that any resource identified by any of the identified real-time search results was updated. 31. The system of claim 30 , wherein identifying real-time search results that are responsive to the re-submitted query includes retrieving relevant real-time search results from a search results cache that caches search results responsive to the query.